Written by Rueben Antman Friday, 30 September 2005 '02 Flashers System Maintenance
Many common signal and flasher problems can be dealt with with some simple maintenance of the electrical system itself. Often this is prodded by some little electrical quirk that one is trying to get rid of. In my case, the "B" light on my dash was not blinking when I had my turn signal on. Because I knew I had a good flasher relay, I was able to eliminate that and just deal with the rest of the system.
This is based on what I found on my '72 2002, but hopefully these tips will apply to all '02ers.
The first thing I did is replace all my bulbs with OEM bulbs purchased from the BMW dealer (OSRAM is the manufacturer I believe). These are nice because they have the nickel plated bottom instead of the copper bottom (which tend to be more prone to corrosion as I understand it). I'm sure you can get ones that are just as good elsewhere and pay less, but I wanted to completely eliminate the bulbs as the culprit.
Beginning with the taillights, I cleaned all the contacts on the light housings that the bulbs come into contact with by using some electrical contact cleaner and some fine grit sandpaper. This freshened them up and removed some of the gunk and buildup. On my car, the contacts are actually two doubled-up metal contacts that sit right on top of each other. So I also slid some sandpaper in between them to make sure the connection between them was clean. I also made sure that the turn signal wires were hooked up correctly. Turns out they were already correct, because they went a little haywire when I reversed the wires. You live, and you learn
Moving next to the front of the car, I made sure that the wiring on the turn signal units were correct. Correct means that the blue wire goes to the larger turn signal bulb, and the grey wire goes to the smaller parking light bulb. The wiring on my right side was reversed. Once I corrected the wiring, the blinker light on my dash magically began working when I signaled to the right. My left side wiring was already correct, but it didn't start working until after I cleaned the rear bulb contact.
An important note for testing the front turn signals: the screws that hold the lens to the car are also the means of grounding for the lights. So if you try to test your turn signals while the signal housing is not attached to the car, you'll get erratic behavior due to lack of proper grounding. This plagued me for a while until it dawned on me.
This has little to do with the signals directly, but its important in general for all electrical issues: I didn't have the correct cable for the negative battery connection. My old cable was a single braided cable that attached only to the engine block. The proper (OEM) cable is a braided cable that splits into two, one piece that goes to the engine block and the other smaller one that attaches to the side of the battery tray for the chassis ground. I ordered one from my local parts shop and installed it. It didn't actually make a difference in this case because I had already taken other steps to properly ground my fuel/temp gauge anyway, but I'm glad that I did it nonetheless for the obvious other benefits of having proper grounding on the car. (Thanks to those on the board who clued me in to the proper cable).
So, in summary, whether or not your blinker works properly can be a combination of things, or can be just one thing. But by covering all your bases you're bound to fix the problem somewhere in there. This happens to be the combo that worked for me. It's really important to make sure the wiring is correct on both the front and rear housings. Once you've eliminated these basic issues, you can tackle the sticky stuff like the flasher relay and hazard switch itself.
If you have any questions, feel free to post them to the Message Board!