NC Bosectomy

Idiot’s Guide to Bosectomy using Stock Wiring

Buying / Unpacking

Head Unit: Clarion VX404 – I narrowed it down to this one or a Pioneer due to features and also due to how many MP3s it would allow on SD Cards / USB sticks. This one was by far the highest - 65,535 folders and 65,535 files allowed.

NC Bosectomy Clarion VX404 Box.jpg NC Bosectomy Clarion VX404 Front.jpg

Amplifier: Alpine KTP-445U – This was a no brainer as it was small enough to fit in the same spot as the Bose amp and didn’t require running a separate cable to the battery (since the Bose amp is on a 20 amp fuse, more than enough for this). Note: Make sure you get the KTP-445U NOT the KTP-445A.

NC Bosectomy Alpine Box.jpg NC Bosectomy Back Of Amp.jpg

Speakers: Polk DB6501 - I’m a fan of Polk products and the DBs get recommended on Miata.net a lot, so I decided on this component set. They can handle a good amount of power, and while the Alpine amp isn’t super powerful, it’s bridged 90 watts RMS x 2 should be plenty to make these sound good.

NC Bosectomy Polk Box.jpg NC Bosectomy Polk DB6501.jpg

Extras: Access ASWC-1, 2 (yes TWO) Metra connectors, DIYBypass.com parking brake bypass, Aux-In / USB outlet, PVC speaker adapters (from car-speaker-adapters.com). You’ll also need a lot of electrical tape – I used almost 2 rolls.

NC Bosectomy Extras.jpg NC Bosectomy Speaker Adapters.jpg

Also, here's a link on where to buy the Aux-In/USB outlet: http://www.amazon.com/gp/product/B00I21W6N8/ref=oh_aui_detailpage_o01_s01?ie=UTF8&psc=1&tag=viglink20337-20

Planning and Diagrams

Resist the urge to skip this part, as car audio wiring can be fairly complex and going in with a good game plan laid out will make things a lot easier in the long run.

Head Unit Wiring Diagram

This one is fairly straight forward, the only exception is the extra pins you have to add. For some reason Metra doesn’t give you the pins (1N and 1P) for the steering wheel controls on their harness. I was thinking I could steal them from the rear speaker pins that I wouldn’t be using, but unfortunately those are bigger pins and you can’t use those. So you have to buy two Metra adapters and steal two of the small pins out of the second one. I chose to steal the Blue and Blue/white wires from the second adapter - you can do this by using a terminal tool or just a small jeweler’s screwdriver.

Orange wire note: This may not actually go to anything. The Terminal Layout lists terminal 1E as going to TNS+ (the dimmer), but the wiring diagram doesn’t list a 1E anywhere. I figured it wouldn’t hurt to wire it up just in case.

The following 3 pages include my diagram as well as the stock head unit layouts from the Mazda NC1 service manual.

NC Bosectomy Head Unit Diagram.jpg
NC1 Head Unit Terminal Diagram.gif
NC1 Audio Wiring Diagram1.jpg

Amplifier Wiring Diagram

This one is more complicated than the head unit, as you have to match up the stock amplifier wiring with what you’re going to need on the new one. The Bose amplifier has almost 30 wires going into it, but we’ll actually only be using 15 of them (unless you want to run rear speakers).

In my case I’m not wiring any rear speakers and I’m switching the Alpine amplifier to 2 channel / bridged mode. If you wanted to run rear speakers you could keep the Alpine in 4 channel mode and then connect the green and purple wires from the Alpine with the rear speaker wiring taken from the Bose amplifier (more on this in the amplifier install section).

Amplifier speaker level inputs – I’m choosing to just use speaker level inputs on the Alpine amplifier, so I’m going to cut the RCA jacks that it comes with and just solder the individual wires together. If you wanted to go the RCA jack route you could buy 4 male RCA solder jacks. You would then need to solder two jacks onto the Gray/Gray-Black and White/White-Black wires on the Metra harness and connect them to the front RCA outputs on the head unit. Then on the other side solder the jacks onto Pins 1T & 1R and Pins 1P & 1N and then attach them to the Alpine RCA front input jacks. Youtube has many videos on how to solder RCA jacks.

Door speaker wire note – the Bose amplifier actually has 4 wires (2 sets) for each door. In the NC1 they combine them downstream from the amp for some reason and then split them back out again when they get to the door. In the NC2 they are separate wires all the way over to the doors. Since I’m running a component set I really only need one set of wires to go to the door. So I decided to just double up both wires and attach them to the corresponding single wire on the amplifier. This helps with current carrying ability.

The following 4 pages contain my amplifier wiring diagram and then a few relevant pages from the Mazda NC1 service manual.

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NC1 Bose Amp Terminal Diagram.gif
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NC1 Audio Wiring Diagram3.jpg


I found it easiest to break everything down into different parts and do a little at a time each day. This really makes all of this work seem easier as you only focus on one thing at a time. I started with installing the speakers and dynamatting the doors. I’m slow so I only managed 1 door per day.

1) Disconnect the negative terminal on the battery. Do this before EVERY audio installation you do. Not only does this make you safer, it also prevents you from blowing fuses and other related problems. I usually pull the connection terminal back behind the plastic so there is no way it could make any kind of connection again.

NC Bosectomy Disconnect Battery.jpg

2) Remove the inner door card. There are many instructions for this on Miata.net so I won’t go over it again. 3 screws and then just give the door a yank from somewhere along the bottom for the plastic clips to come out. It’s a good idea to have at least 2 or 3 extra plastic clips in case one breaks (Mazda part # GJ6A-68-AB1).

3) In order to properly Dynamat (or whatever equivalent you want to use), we also have to remove the black plastic section. If you don’t get Dynamat behind this it will vibrate like crazy on every good bass note (as it does with the Bose woofers). You’ll have to take out the woofer, then there are about fifteen 10 mm bolts and a couple of plastic clips that hold the black plastic piece on. After those are all removed you have to remove 3 cable connectors (see following pictures for the cable connectors removed).

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NC Bosectomy Door Connector 2.jpg
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4) Once you have every bolt removed and cable disconnected, you can now pull the plastic section off. The part around the speaker has some sticky foam on it, so you have to kind of pull / peel that off. You will not be able to remove the wire loom coming into the door, so you can just kind of rotate the whole thing around and sit it on the seat.

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5) Now you should have a (mostly) bare door that you can apply Dynamat to. My door was a little dusty / dirty so I went ahead and wiped it down with some alcohol to help the Dynamat adhere.

NC Bosectomy Bare Door.jpg

6) I hung the Dynamat up with some blue painter’s tape to get an idea of where I needed to cut edges and holes. I used my fingernails to roughly mark where the holes were.

NC Bosectomy Dynamat Taped Up.jpg

7) Then I removed it from the door and cut it with a utility knife on the driveway. Don’t worry if the holes aren’t quite big enough, as you can trim it after putting it back on the door. In fact, I’d recommend trimming a little less than you think is needed.

NC Bosectomy Dynamat Cutting.jpg

8) Time to peel and stick it to the door. I mainly focused on Dynamatting the part of the door that is behind the black plastic section, as this is the part that vibrates the most. You can do the upper part of the door as well if you’d like, however.

NC Bosectomy Dynamat Applied.jpg

9) I also went ahead and put some extra Dynamat around the inside rim of the woofer area on the plastic piece.

NC Bosectomy Dynamat Speaker Area.jpg

10) Now comes the fun part. You have to go back and find all of the little holes for the bolts, plastic clips and wire connectors and cut the Dynamat around them. You can always hold the black plastic piece and / or the door card up to it to make sure you got all of them. There are also some larger bolts that hold on the window frame, so I cut holes around those as well in case I ever needed to get to them in the future.

NC Bosectomy Dynamat Applied 2.jpg

Note: You may notice that I have some Dynamat inside the door behind the woofer. I did this during a prior installation, but found it didn’t really accomplish anything, so my recommendation is not to bother doing this at all. Just focus on Dynamatting the door area that sits behind the plastic section.

11) Now you can put the plastic section back on the door and bolt it all back up again.

Speaker Installation

1) Time for the speakers. I started by installing the 8” to 6.5” speaker adapter using the 4 screws that came off from the Bose woofer. Then you need to start peeling back all of the wire insulation / electrical tape around the center / near the woofer. This will reveal the speaker wiring. Warning – this makes your hands VERY sticky.

NC Bosectomy Door Wiring.jpg

2) I decided to tuck the crossover in the area that indents and is only a foot away from the wiring (picture below actually shows the passenger side). I won’t take credit for this idea – I got it from Joe the Woodworker who used to be on Miata.net. He has a whole web site with his write up on installing these Polks here: http://www.joewoodworker.com/miazda

NC Bosectomy Door Wire Cleanup.jpg

3) So to mount the crossover, I kind of slid it into the area, making sure the bottom was sitting in / on the large plastic groove below it. I then took the cover off of the crossover (it’s a pain, but mainly you just yank it off from the side with the switch on it, I cut my hand the first time I did this, so fair warning). It has two holes that you can use to mount it. I put it into position, then carefully used a drill with a very small drill bit to drill a couple of small starter holes in the plastic. If you recall from when we took the door apart, there’s actually nothing behind this piece for a good 4 or 5 inches (then you get to the window mount area).

NC Bosectomy Mounting Crossover'.jpg
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4) After that, tighten both screws into the door and slide the cover back under the wire and put it back on the crossover. Note: some of you may not have this wire in your way – I think it depends on what options are installed on your car. You can also use this moment to set the crossover’s tweeter level. I originally set mine to 0 dB, but found later I liked it better on -3 dB instead.

NC Bosectomy Crossover Mounted.jpg

5) So back to those wires. You’re going to want to clip off the molex connectors that are currently on them and / or even just clip the wiring further back so it matches up where the crossover is. If you’d rather keep the extra length of cable just in case you can always just tie it up further back as well. There will actually be four wires as I mentioned earlier – two Green and two Red (or two Yellow/Red and two White/Black if it’s the passenger door). The Green cable splits much later than the Red cable (you can see in the earlier picture where the blue electrical tape is from where Mazda taps / splits the wiring). Since it was so long, I just went ahead and clipped the Green further back where it was just one wire. The Red cable I left with the two wires. I stripped all 3 wires back about the length of the screw terminals on the crossover. Prior to connecting them up, I went ahead and combined the Red wires (and Green if you kept both) and ran a little solder on the tips to join them together. I also put a little solder on the single Green wire as well so it would connect better to the crossover. This step probably isn’t necessary, but it makes me feel better smile

NC Bosectomy Solder Wire Tips.jpg

6) After the wires cool for a minute, go ahead and connect them up to the crossover. Green goes to negative, Reds go to positive. Note: this is different than some earlier NC1 instructions mentioned. But according to Mazda’s service manual this is correct. For our purposes, however, it doesn’t really matter, as long as you wire it consistently on the speaker and amplifier ends then everything will be in phase.

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7) Next I began wiring up the woofer, using Polk’s included cables. For the Polk cables, the Gray with Red stripe is the positive cable, the Gray with no stripe is the negative. You can usually tell by the size of the quick disconnects (larger one is positive). Remember to route it through the indent in the plastic prior to connecting it up. Also, as an extra precaution I wrapped a good bit of the wire in electrical tape as some of it was going inside the outer door area where things can get wet.

NC Bosectomy Wiring Woofer.jpg

8) Now time to mount the woofer. I put the XTC baffle in between – remember to cut out at least the bottom third of the baffle to allow air into the woofer, but still protect it from water coming into the door. Then go ahead and connect the woofer cables up and screw it into place. Unfortunately, I never found an easy way to do this – you are kind of stuck cursing and fumbling around to find the holes in the adapter when they are covered by the foam baffle.

NC Bosectomy Mounting Woofer.jpg

9) Once the woofer is all mounted, you can now re-wrap all of the cabling with electrical tape and re-route it back to the plastic areas they were behind / around before.

NC Bosectomy Taping Up Wiring.jpg

10) For the tweeter mounting (which goes on the door card), I found that the adapter didn’t quite fit in the existing spot, so I had to trim the edges on them a bit in order for it to mount with the existing screw holes.

NC Bosectomy Tweeter Adapter.jpg

11) After the adapter was trimmed, I discovered there really wasn’t much room in between the adapter and the speaker grille on the door. So all of the mounts that came with the Polk tweeters were too big. I resorted to trimming a little of the adapter material where the wires came out of the tweeter, then using some 3M indoor/outdoor tape to mount the tweeter to the adapter. You don’t need to go too nuts with the 3M tape, as honestly it’s a tight fit and the tweeter would probably stay even without it. For final mounting, I had to use slightly longer screws than were already on the door in order to get them to reach the screw holes.

NC Bosectomy Mounting Tweeter.jpg
NC Bosectomy Tweeter Mounted.jpg

12) You can’t fully hook up the tweeter until you put the door back together as it’s attached to the door card. You can again use the quick disconnects that came with the speakers, or like I did just attach the stripped ends to the crossover just before you put the door back together (you will also need some kind of tie to wrap up the extra cable slack or just trim the cable so it has no slack). As before though, Gray with Red stripe goes to positive, Gray with no stripe to negative. I went ahead and wrapped all of the tweeter wiring in electrical tape as well (yes I do own stock in electrical tape companies smile).

13) One final step before you can put the door back together. We have to trim the foam that goes in the area that now contains the crossover. I held the door card up to the door and matched where the closest trim clip was. From there I got an idea of how much I needed to trim off and marked it with a pencil. I then used a drywall saw to cut it down to size (cutting it is very messy, so you may want a small vacuum on hand).

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NC Bosectomy Cutting Foam.jpg

14) Once it’s trimmed, you can put the door back together again. Hook up the tweeter, tie up any cabling if needed and snap everything back in place. Put the 3 screws back in and you are done. Now repeat on the passenger side door! smile

Head Unit Wiring

This step is nice because you don’t actually have to be in the car to do it. I wired and soldered up the head unit while sitting at my kitchen table (with stuff to cover it and protect from solder of course).

1) I started by pulling out everything I would need. Running clock wise / left to right in the picture - the Metra harness, the Axxess ASWC harness, the parking brake bypass resistor and the head unit wiring harness.

NC Bosectomy Head Unit Wires.jpg

2) Starting with the Metra harness, as I mentioned earlier in the guide, we need to steal 2 pins from the extra Metra harness. In the first picture I circled where the pins are missing (I upped the contrast and brightness so you could see things easier):

NC Bosectomy Metra Missing Pins.jpg

3) On the extra Metra harness, you’re going to want to take a terminal tool or a jeweler’s screwdriver and push it into the larger holes above the pins. This will push the clip down so you can then pull the wire out from the other side. From there you can then bend the metal clip back up slightly and then re-insert in the other Metra harness. Make sure it stays when you try to pull it out. If not pull it out and bend the metal clip up higher so it grabs better.

NC Bosectomy Remove Terminals2.jpg
NC Bosectomy  Remove Terminals2.jpg

When done the Metra harness should now look like this:

NC Bosectomy Extra Pins Inserted.jpg

4) Now time to solder / connect it all up! Follow the head unit diagram back in the planning section and start connecting all of the wires. I prefer soldering, but butt splices would also work (except maybe on the ground wire, where you’ll have to find something to connect 5 different wires together). When soldering I like to heat shrink each connection and then wrap it with electrical tape. If you’ve never soldered before, you can find a lot of good Youtube videos on how to do so. I recommend a good 35 watt or higher soldering iron and some flux.

5) When done with soldering / connecting everything up, I went ahead and wrapped it all together with some ties to help hold it all together and aid in preventing things from shaking loose down the road. You can also see I pulled out the extra pins that I wasn’t using (the rear channels in the top right) just so I wouldn’t have more wires to tape up.

NC Bosectomy Head Unit Wiring Finished.jpg

Head Unit Installation

1) Pull out the Metra 99-7506 head unit installation kit (or Scosche if you bought that one instead). Note: the NC2 has a different mounting kit as Mazda apparently slightly changed the position of the head unit.

2) For starters they have you attach 4 white plastic clips to the back of it. You just push them in until they click.

NC Bosectomy Metra White Clips.jpg

3) If you have a double-din unit you need to cut out the middle section. I used a pair of wire cutters. Cut it where they have lines in the plastic, as you need a bit of the end to stick out to attach the sides to it.

NC Bosectomy Metra DIN.jpg

4) Insert the two larger sides into the plastic L pieces on each end. If you have a single din unit, you’ll obviously insert the new pocket and the smaller plastic pieces for single din mounting.

NC Bosectomy Insert Head Unit Sides.jpg

5) Put the head unit into the Metra kit (I used the head unit box to hold the back of the head unit and make it easier to adjust). I took a little time to play around with positioning the head unit to see where I liked it. I decided to mount it a little further back so the head unit sat flush with the Metra kit as this looked cleaner to me. I then found 4 available holes to put the included screws in (the fourth one is hidden behind the front in this picture).

NC Bosectomy Metra Mounting.jpg

6) Once the head unit is mounted, time to pull out all of the head unit cabling and connect it up. The included RCA connectors already had plastic caps on them, so I initially wrapped them all up with electrical tape. After I went to install it I discovered I didn’t quite have enough room to fit it all behind the head unit. So I went back and popped all of the pins / wires for the RCAs out of the harness thereby eliminating the need to stuff them somewhere. Unfortunately in my case I couldn’t just skip the whole connector, as I used ONE of the pins for the steering wheel control connector (the head phone jack in the picture).

NC Bosectomy Wiring Head Unit2.jpg

7) As part of this install, I also decided to switch out my cigarette lighter for an AUX-IN and USB connector, so I connected up the RCAs and USB to the back of the Aux-in/USB unit I bought. I made another small mistake here as I went ahead and taped up the USB and RCA connectors to secure them, but discovered that it’s better to do this when you install the head unit in the car as then you can figure out where everything is going to go first.

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8) Time to go to the car. Disconnect the negative terminal on the battery as per usual. Remove the stock head unit. There are many write ups on this on Miata.net so I won’t go into the details here – just pop the sides off and remove the 2 screws holding it on and curse and pitch a fit while you blindly remove the back connectors by shoving your hand in through the glove compartment. In short fun for the whole family smile

9) Once you’ve removed the stock unit, you’ll need to steal the A/C controls off of it. Just four screws on the back and pull it out. Make sure you put it the correct way on the Metra kit (I almost put mine in upside down). Then attach the four screws.

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NC Bosectomy Inserting AC Controls.jpg

10) Installation time. Bring the head unit and all of the wiring out to the car. Since I was replacing the cigarette lighter, I had to remove the center console and remove the piece the cigarette lighter attached to (there are two screws on the left and right you need to take out). If you aren’t doing this you don’t need to remove the center console.

11) If you want to replace your cigarette lighter, you’ll have to pull out the old one. It has a molex connector that you can disconnect – I covered it in electrical tape again so there was no potential of it ever shorting on anything. Then there are some plastic pins around the cigarette lighter that you pull up and can then pop the whole lighter out (forgot to take pictures of this part). Put the new Aux-In/USB in the spot where the old cigarette lighter was and then screw in the included back piece to attach it to the console. There is a spot in the back left corner where you can then sneak the wires up to the head unit area. These then get connected to the rear Aux-In and rear USB ports on the back of the head unit – if you want to do this, make sure the head unit you buy has rear Aux-In and USB inputs.

Note: I didn’t realize this until after, but if you replace the cigarette lighter with the USB/AUX in you take away the ability to attach the tire air compressor that is in the trunk. So, I went ahead and bought a battery clip on cigarette lighter adapter in case I get a flat:


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12) For installing the head unit, I took a box I had and used it as a place to sit the head unit while I figured out the cabling.

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13) Connect the Metra harness into the stock connector and the antenna directly into the back of the head unit. If you had a satellite radio or Aux-in connector that went into the stock unit, you won’t need that one anymore (you may have to replace and / or figure out how to move it to the new head unit). Don’t forget to connect the A/C controls back up as well.

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14) Now the next fun part – figuring out where to stuff all of this wiring. I had to separate all of the wire tying I had done earlier. There are little pocket areas on the left and right of the head unit that I used to put stuff. The Metra connector wires and the Axxess unit I snuck off to the right near the glove compartment. The RCAs and USB for the cigarette lighter adapter I snuck over the left. I tied everything up and cable tied various bits to the car to keep everything from vibrating and / or making noise. The only thing you want to be careful of here is you don’t cover the back fan of the head unit – you can feel the back of it from inside the glove compartment to get an idea how much clearance is back there.

15) Once you’ve got everything properly tucked away, you can now push the unit into place. You have to give it a good shove to get the white plastic connectors to grab in. Remember NOT to push on your LCD when you’re doing this though. Once it’s in and mounted, you may need to reach into the glove compartment area for final tie down of any bits that ended up around there – most notably the Axxess PAC unit I had to tie down somewhere.

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16) Done – time to test. Hook up the battery cable then power it on. Wait a minute or two before testing out the steering wheel connections as it has to auto-recognize the car. After that, the steering wheel controls should now work. My steering wheel controls worked right the first time, but if you’re worried about this part you may want to test prior to fully installing the head unit in so you can watch the LEDs on the Axxess unit itself.

Amplifier Installation

1) In the PRHT (power retractable hard top), the Bose amplifier is located right behind the passenger seat. In the soft top NC it’s further back underneath the soft top itself so you may have to remove the whole back plastic section in order to get to it. I put the PRHT down on my car prior to disconnecting the battery, as it makes it easier to access the panel when you don’t have to squeeze your head under the top.

2) For PRHT owners, start by popping out the plastic cover behind the passenger seat – it’s just held on with some plastic clips on the top. You can then rotate it down and pull it out of the bottom attachment points. From there you can peel up the foam cover and reveal the Bose amplifier. Note: it will most likely rip on the left corner when you lift it all the way up. There doesn’t appear to be a way to prevent this as it’s apparently glued in the upper left corner. Possibly if you used a putty knife or razor to scrape underneath it first you might be able to lift it without tearing the foam?

NC Bosectomy Amplifier Cover.jpg
NC Bosectomy Bose Amplifier.jpg

3) I then grabbed some tape and taped the foam cover up so it would be out of the way. From there you take off the four 10 mm bolts that hold it in. You can then pull the whole unit down. I found that a bucket behind my passenger seat would hold things up while I worked on them. I later added a box on top of the bucket to bring the height up a bit as well.

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4) From there you’ll probably need a small flat head screwdriver to push down hard on the tabs to remove the molex connectors. Not sure what type of connectors Mazda uses in their cars, but they are seriously hard to remove sometimes!

5) Now pull out the Alpine amplifier and cables. First we’ll have to set the dip switches on the back of the Alpine KTP-445U. There’s a small rubber cover on the back – pull that out and the dip switches are underneath. In my case I was only running two channels and hooking it up with speaker level inputs, so I set dip switch 5 up and dip switch 6 down. And since I’m not running a subwoofer, I left the high pass filter (HPF) on the default setting of Off. You can usually tweak this in your aftermarket head unit settings as well later, though.

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6) Next up we need to set the gain on the amplifier. I started out turning it all the way down since we are using speaker level inputs (sorry for the blurry pics but apparently this was the only one I took). Later when I was tweaking the system I turned the gain up two marks - around 10:00 if this were a clock face.

NC Bosectomy Alpine Gain Controls.jpg

7) So when I went to mount the amplifier I ran into a few issues. You could potentially sit it on the shelf right behind the metal bracket, however the Mazda service diagram refers to the foam cover as a “water shroud.” So I figured this was to protect the amplifier from any water coming off the PRHT if you put the top down wet. Since I do actually do this on occasion, I then decided to mount the amplifier higher up so it would be covered by the shroud.

8) To mount it higher up, we have a nice metal bracket on the left to attach it to, but nothing on the right. My wife came up with the idea to use some metal plumber’s tape (aka bracket tape). I used the 10 mm bolts from before and inserted them backwards to mount the plumber’s tape. Note: you can also see in this picture just how close the PRHT gets to the amplifier when the top is down.

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9) I put the Alpine amplifier up there and lined it up with two of the bracket tape holes and then marked two spots on the left bracket where I would drill holes for the other side. I circled the two holes I drilled in red – the upper one you can’t see because the foam flaps down and covers it.

NC Bosectomy Amp Mounting.jpg

10) Before we can mount the amplifier we need to wire it up, of course. So time to break out the wire cutters, strippers and soldering iron (or again butt splices if you prefer). Here’s my set up with the box sitting on top of the bucket so I could lay the wires out for soldering:

NC Bosectomy Amp Soldering Setup.jpg

1) Since we’re using speaker-level inputs, you’ll need to clip off the front channel RCA ends (Gray and White). I also taped up the RCAs for the rear channels (Green and Violet). If you were using rear speakers, you’d want to clip the RCAs for those as well. For the fronts follow my amplifier wiring diagram that was back in the planning section. For the rears amp Violet goes to harness Green / Black, amp Violet / Black goes to harness Green / Orange. Then amp Green goes to harness Blue / Yellow, amp Green / Black goes to harness Yellow.

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2) For the rest of the wiring you can again follow my amplifier diagram in the planning section. If you wanted rear speakers the outputs get a little more interesting here. Mazda once again only runs 1 set of wires over to both rear speakers and then splits the wires when they get there. So you could potentially just wire up one of the rear channels (but definitely not both!) to that one set of wires (Pin 1W Pink is the negative and Pin 1U Violet is the positive) and into two 4 ohm 3.5” speakers. This would present the amplifier with a 2 ohm load (which it is capable of unbridged). You’d then be feeding about 45 watts into both rear speakers and 90 watts into both of the fronts so that would probably make for a good balance. Alternatively you could run new wiring to each individual rear speaker and get the full 2 channels / 90 watts in the rear.

3) Once everything was wired up, I went to town with the electrical tape (again) and wrapped everything up, since once again this area is semi out in the elements. I also wrapped up the old Bose connectors and stuffed them and tied them back there as well.

NC Bosectomy Amplifier Wiring Wrapped.jpg

4) For final mounting of the amplifier I connected up all of the harnesses and snuck it back behind the brackets and lined it up with the holes I had drilled earlier. I drilled small holes and used some small nuts and bolts I had lying around to mount it. The hardest part was getting my fingers into the back side to get the nuts to thread. Much cursing was involved in this process, so if you can come up with a better (or even just different) method, I’d suggest you try it first instead of mine smile

5) I then finished it off by using the cable ties that came included with the amplifier. I doubled up two of them and ran them through the available bottom left hole and attached it to the amplifier as an extra tie down for it. I used the rest of the cable ties to wrap up some of the cabling so it wouldn’t make any noise. Since the metal bracket tape is kind of sharp I decided to wrap it in electrical tape as well so I wouldn’t have to worry about it cutting into any insulation.

NC Bosectomy Final Amp Mounting.jpg

6) Before you put it all back together you may want to adjust the amplifier gain to your liking. With the way I mounted it you kind of have to do it by feel, however, so possibly do this step before you fully mount the amplifier.

7) Once done adjusting, pull the foam flap back down and tuck it back into the cubby hole. I electrical taped the rip in the foam (because of course I did smile). Then take the plastic cover and insert it into the bottom and rotate it up and snap the top in place. The amplifier is now installed!

Installation Finished / Tweaking

So now that everything is installed, sit back and begin to enjoy your new sound system. I started tweaking the colors on the Clarion to get it to match the red lighting that the NC has. I also tried out my Aux-In / USB connector to make sure it worked and charged my phone.

NC Bosectomy Final Head Unit.jpg
NC Bosectomy Final USB Aux In.jpg

Upon running through a few songs I determined a little equalization would be needed as some rock songs sounded a bit harsh. So I broke out my laptop and some free spectrum analyzer software I’ve used before. The software I like is called SynRTA and can be found at this web site:


You can have it create a pink noise .WAV file that you can then burn to CD. From there a laptop and a decent microphone are all you really need. You’ll want to tape up the microphone so it sits directly in front of the tweeter (as highs are very directional, but mids/bass not as much). For back to back testing you’ll also want to make sure you set the volume the same so it will be easier to compare. Open the program and it will start showing you the frequency response - you’ll want to switch the vertical range to 50 dB. I like to save a few results to .CSV files and open them in Excel and do a scatter plot of them to get an idea of how they compare and make decisions on how to adjust the equalizer settings.

What I found was that either the Polk DB6501s were a little strong in the 5,000-8,000 Hz range or something with the location of the speakers in the NC was causing a spike here. This was making guitars sound a bit harsh and drowning out some of the mids and bass.

At any rate, I played around with the equalizer on the Clarion (it has a 3 band parametric equalizer similar to many aftermarket head units). I found that if I set the Treble setting to center around 5 khz then widened the Q to 0.7 (the smaller the Q value the wider the range it affects) and brought it down about -4 dBs that leveled the problem area out nicely. Here’s an example of my final Excel graph. The blue line is the Polks un-equalized, the green line is post equalization. I also took a screen shot of how I typically set the X axis in Excel.

NC Bosectomy Equalization.jpg
NC Bosectomy ExcelSettings.jpg

After fixing the problem area, the speakers sounded awesome. The sound is now much more balanced than it ever was with the Bose. And I can now hear the separate instrumentation I always hear on my home speakers but could never here in my car.

I’m even mildly impressed with this tiny Alpine amplifier – if you crank it, it gets LOUD. Way louder than I’d ever want to listen to it.

The End

I hope this guide was helpful to audio noobs like I was once myself. It’s a lot of work (I spread it out over the course of 4 days), but the end results are worth it to me.