Although this wasn't the hardest part of the installation, it did require the most planning. Since I wanted to retain the original head unit, I had to figure out how I was going to make everything work while not losing a whole bunch of space mounting extra components.
I started by mapping out as many wires as I could from the harness that plugged into the BOSE amp. There are 3 molex-type plugs going into the Bose amp. They seem to go in order from left->right by wire gauge - - after a good bit of trial & error, I've mapped out the important wires. There are some that I still haven't identified, but I got all the important ones I needed.
1. Left plug - very small wires. (About Cat-3 size) Carries signal from head unit.
- Yellow/Yellow stripe - Left Front
- Purple/Purple stripe - Right Front
- Grey/Grey Orange stripe - Left Rear
- Green/Green stripe - Left Rear
2. Middle Plug - roughly 16 gauge wire, with a few smaller ones interspersed. Mainly speaker outputs -
- Red with Yellow Stripe - +12v Amp Turn-on signal (from head unit)
- Black - Ground to head unit
- Yellow/Yellow stripe - Front Left (not used in my install)
- Purple/Purple stripe - Front Right (not used in my install)
- Brown Yellow Stripe/Brown Red Stripe -Right A Pillar Tweeter
- White Blue Stripe/White Green Stripe - Left A Pillar Tweeter
There were quite a few other wires on this plug, but it seemed that the rear speaker output used some sort of funky common ground? Since was replacing the speaker wire anyway, I didn't bother trying to identify them all.
3. Right Plug - Largest wires. Power & subwoofer, were what I identified. Again, there were other wires, but these are the ones I needed:
- Red/White Stripe - +12V always on
- Black - Ground to car body
- White Black Stripe/White Red Stripe - Subwoofer Out (not used in my install)
Since I was going from speaker-level wiring (albeit tiny wires!) to preamp level, I needed a line-level converter. I chose the AudioControl LC6i, since it seemed to do everything I wanted and was reasonably priced.
I'd already picked out the Rockford Fosgate P400-4 channel amp and a 1-farad stiffening capacitor, but trying to figure out where to mount all this was tricky. After careful measurement, I decided to mount the amp & capacitor under the passenger seat... since I wasn't going to need the BOSE subwoofer anymore.
First, the LOC:
1. Carefully pry off the plastic cover from the BOSE amp in the trunk area.
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2. Remove 3 10mm bolts holding it to the mounting bracket.
3. Unplug the 3 wire harnesses from under the BOSE amp.
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4. Remove 3 10mm nuts holding the mounting bracket onto the frame.
I used a thin piece of wood to create a simple mount that connects the LOC to the existing bracket. Then came the fun part - hooking it up!
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Being a computer geek, I noticed that the holes on the harness carrying signal from the head unit looked to be about the same size & spacing as the holes on an ATAPI cable. Turns out, they are *EXACTLY* the same size & spacing - which made things a lot easier.
I first obtained a 40-pin male to male IDE/ATAPI coupler. I got mine from work, but they can be found on eBay for only $2-4. There are 12 "holes" in the existing harness, so I used a sharp knife to cut the coupler, leaving 12 pins.
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Then, using some old jumpers and motherboard connectors, I fabricated a plug that would connect into the existing harness. A couple of old audio cables from a computer CD ROM would work as well. I could have also cut the wires, but this way I could preserve the harness & reattach the BOSE when I eventually sell the car.
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Now it was time to hook it up to the LOC. It was tricky - I'd identified which wires went with which channel, but I hadn't identified which was positive and which was negative. You'd think that if you stick with all solid=positive, striped=negative you'd be safe.... but BOSE apparently doesn't like to do things that way. What seemed to work well for me is an alternating pattern:
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| LF+ | RF- | LR+ | RR- |
| LF- | RF+ | LR- | RR+ |
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I tapped into the existing power, ground, and remote-on from the harness. Once I was satisfied that I had wired everything correctly, I used a liberal dose of duct tape to hold all the wires in place. Low-tech, but it did the trick?
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I then ran the RCA cables, routed all the wires, and mounted the LOC neatly into place.