I'll try to make this quick. The background is that I'm installing a carputer in the trunk (boot) of my 2003 E46 325i sedan. I'm routing the computer into the stock sound system (non-H/K). I needed an accessory wire, but everything I read online says that you have to cut the white wire in the amplifier harness to get an accessory wire. I didn't want to go cutting into a harness that is still in use, what with all of those spare harnesses in the trunk.

So I stupidly went and cut a wiring harness off looking for a 12 volt switched line. I didn't find one, but I found an 11 volt line switched line which was good enough to start the computer.

I got the computer installed and went for a test drive and noticed some weird things going on. About fifteen minutes down the road my head unit just turned itself off. I turned it back on and it stayed on for another half hour or so and then turned itself off again. Then when I parked and turned the car off, the head unit stayed on, which it shouldn't, of course.

So I opened the trunk and disconnected the computer's accessory wire from the 11 volt wire I was using. Then went for another test drive. And this is where things got interesting. While going 70mph down the freeway my car all of a sudden started stuttering. It felt like the brakes were being tapped. Every time it happened it would instantly slow the car down about five miles per hour and then quickly go back to normal. It felt like either quick stabs of the brakes or engine spark retarding, which lead me to wonder if the DSC system was acting up.

Of course this definitely alarmed me. I started to get curious about what I actually cut and just how badly I screwed up my car. The wiring harness that I chopped off is the 26 pin (2 rows of 13) blue harness with a black cap on it. From what I've read online, this is the bluetooth harness. So I took a closer look at it and took the cap off. It was at this point that I noticed that the cap was completing circuits between wires in the harness. So, using the cut-off harness as a reference and tracing wires back, I spliced together every wire that the harness cap was connecting (basically wired it up just like it was, only without the harness).

Now the car runs and acts fine, but the stereo is still weird. On the way to work today it randomly shut down again. And I have to manually turn it off and on when I start or shut-off the car. Like it's got constant power and isn't listening to the accessory lead.

So my questions are:

Why would clipping a harness off of an optional accessory that I don't even have adversely affect something as critical as the power train? That seems like a strange way to wire up a car.
Even though I've now got it hooked up exactly how it was before, it still acts funny. I'm guessing I've damaged the head unit. What do you think?
Can anyone point me towards a pinout for this harness? Here's what I've got so far:


Pin 1: Red w/ yellow stripe
Pin 2: empty
Pin 3: empty
Pin 4: empty
Pin 5: empty
Pin 6: empty
Pin 7: empty
Pin 8: Solid black
Pin 9: Solid yellow
Pin 10: Solid black
Pin 11: Solid yellow
Pin 12: Solid yellow
Pin 13: Solid black

Pin 14: Solid brown (at least I know this one: ground)
Pin 15: empty
Pin 16: empty
Pin 17: empty
Pin 18: Solid white
Pin 19: empty
Pin 20: empty
Pin 21: White w/ red stripe
Pin 22: Solid black
Pin 23: Solid white
Pin 24: Purple w/ white stripe
Pin 25: Black w/ white stripe
Pin 26: Black w/ brown stripe

Now, this part I'm only 90% sure on, but as far as I can tell, the cap on the harness was bridging
Pin 8 to Pin 10
Pin 9 to Pin 11
Pin 12 to Pin 25
Pin 13 to Pin 26
Pin 18 to Pin 23
Pin 21 to Pin 22
and I've spliced it back together this way. Didn't seem to solve ALL of the problems, though...

Anyway, you can feel free to flame away on me for this one. I know better than this. It was just getting late and I was getting impatient to get it running and cut corners I shouldn't have.

Thanks for any help you can give me. :help :help :help :(

wow, this might be above the heads of the car audio and electronics forum. i would suggest posting this in more a car mechanics forum because they might know right away what you did. The cutting out of the engine almost sounds like what happens when the speed limiter cuts in (mines at 131 :-D).
I was gonna look in m bentley manual but i left it in my car which is a 15 min walk away.

i vote for coinsidence (sp?)

Well, given the task you were attempting you really should have had a wring shcematic for the car before you started all of this. If you had a Bently Manual, you would have had all of that information.

My guess with your stereo problems now is that there's a bad connection. Recheck all of your wiring.

Thanks for the input, guys.
Now that I think about it, I may know what is going on with the stereo (although I can't explain why). Under normal operation, the stereo will shut down when the car is powered off. But it is still possible after that point to manually turn the stereo back on by pressing the power button even when the keys aren't in the ignition. The stereo will play for about twenty minutes, if I remember correctly, and then shut down on its own again. This is exactly what my stereo is doing. In other words, it's acting as if it had no accessory wire going into it at all. This has me stumped, though. I never touched the head unit, so why would IT suddenly act as though I've yanked a wire from it? ESPECIALLY after I put it back how it was!

Also, I'm still baffled as to how I was able to affect the drivetrain by clipping a puny, unused acessory harness.

As far as checking the connections, there's only one thing I broke into from the factory setup and that is this harness, which I have now returned back to how it was. That the problem persists baffles and stumps me. But, as you said, I may just have a loose wire or reconnected it wrong.
I'll go out in the rain and check the connections again to make sure. If I'm lucky I'll electricute myself and not have to deal with this....