Horn sticking/interior light flicker

[acrossthec]

First post on the board, might as well make it troubleshooting question. Here goes:

Bought an '04 M3 Hatch about a month ago. Haven't really had any problems with it, but have noticed a few glitches here and there. For instance, every once and while, maybe 4 or 5 times total in the last month, as I'm cruising along, the dash/stereo lights flicker on/off, and the wipers will pause (if they're going). Didn't think too much of it, since it's probably hard to diagnose a problem just from "hey, my lights flickered".

Then Sunday, out driving downtown after the gold medal game (and what a game!), honking my horn (reasonably, not slamming on it), and the horn sticks, won't turn off. Never mind the bike cops giving me a dirty look, I had no idea what to do. So I turn off the car, in the middle of Yonge St. Turning it off doesn't kill the horn, but when I turn it back on, the interior lights are all messed (i.e. ash tray light, but nothing else, then play with the headlights and the stereo lights come up, but nothing else). Headlights were fine as far as I could tell, just seemed to be in the interior. Turned it off again, played with the headlight switch and the dash dimmer, and suddenly it all pops back to life and the horn stops. No problems with the lights since then, but the horn still likes to stick, particularly when I lock up with the fob.

Only mod on the entire car is a slyflex auxmod. What do you think? Fuses? Take it back to the dealer and let them figure it out? If I can avoid that I will, I use the car quite a bit for work these days and taking it in is a pain. I'm a bit of a noob when it comes to car fixes, this is my first one, though I'm learning fast. Any help/advice is much appreciated.

Thanks!

[Noisy Crow]

Smells like a flaky PJB (car's body computer). $$$. Check the connections at the PJB (it's under the cover under the glovebox) to make sure no one has removed and mis-installed a connector.

*Might* be alternator. But I doubt it...

[sas]

Hello Noisy Crow and hello acrossthec
See here a 1000$ question. Yes it sounds as moisture inside of the PJB.
There is one thing. The internal switch to the horn relay, wipers and the dash dimmer are grounded into the same point.
If there is a bad connection to the body and used the FET switch for horn relay, this switch may work as current generator and you will experience the same effect.
Do check of the connection at ground point 8 as shown on the picture. And do check how the wire is crimped.
http://i709.photobucket.com/albums/ww96/sas2000_album/IlluminationLightAlocation.jpg
It a BlackBlue wire. Also ,near of this ground point the wire is split . Splitter it’s a connector with inserted wires (connects all wires together). Check how wires are
inserted. More stright and more scientific way is a measurement of resistance
between connector J03 pin C and chassis (with disconnected battery must be 0-0.3ohm) if higher then look the ground. It should be a BlackRed wire.
There is pinout for PJB.
http://mazdas247.com/vbb230/attachment.php?attachmentid=146878&d=1237925489

If it doesn’t help and there are signs of water.
I usually use more radical methods, but I’m afraid you can ruin something.
If you can get such stuff as vaseline spray.
You can remove and dry the PJB, spray the vaseline into holes you can find, let it sit on one side, then turn over and do the same for other side.
Do not use the vaseline too excessively, just for sealing and neutralizing the
salt and oxide near possible sources of moisture. Vaseline is safe for electronics. I used it many times, even to seal ultra high frequency connectors and at this moment almost all connectors on my car are sealed by it.
Do photos during this process, to put all at the same place when you will be assembling it back.
Ok, it’s so late.

[acrossthec]

Thanks guys! I appreciate the feedback. I'm going to have a look at it tomorrow with a guy at work and see if I can pin down the problem, and I'll be able to borrow a multimeter if necessary to check resistance. I'll let you know what I find if anything.

I may just end up having the shop look at it, if it's a bigger problem than I can quickly fix. This sort of thing should be covered by the extended warranty I bought (it better be!).

[acrossthec]

Finally managed to get it into the dealership yesterday, and they got back to me today with the problem. Apparently the circuit board on the car's body computer was toasted, and as a result was re-routing current at random, causing the light flicker. The fuses and wiring showed no signs of corrosion, so no moisture damage. Technician said it was a 1/10 000 sort of malfunction. Total cost is going to be just over $1000! Luckily the extended warranty covers it, so it's only $100 deductable. I'm hoping that the dealership will eat the deductable, considering the car has been in my hands for less than two months, though I'm not holding my breath.

Thanks again for the help guys!

[sas]

Glad to hear that. My previous car had the control panel replaced on the second month.
Now, has 14 years and still breathing. Good luck with you car.

[Dave_The_BMXER]

It's not 1/10 000 at all.

My car did the exact same thing with the horn, exact same solution.