I have a 1986 300E with 294k miles on it that I have been maintaining over 24 years. I have a problem with the left stop lamp triggering the bulb check unit light and I have run out of ideas. So far, I have:
1. Replaced the bulbs (Sylvania 7506L) on both sides.
2. Disassembled the rear taillight assemblies, cleaned contacts, resoldered connections, checked grounds. Checked all with an ohmmeter; looks okay.
3. Today I pulled the bulb check unit and checked the resistance back through the wiring to the right and left stop lamps. The resistance was a little over 1 ohm in both cases. Infinity with the bulb removed. Looked okay to me.
4. Replaced the bulb check unit with a used one.
5. The only change with all the above is that the check light used to come on instantly when I stepped on the brake. Now I can step on the brake for a second or so and the light does not come on. As soon as I step on the brake and hold it, the check light comes on in about three seconds.

Any thoughts? I'm out of ideas.

Thanks.

Brent Smith
Snellville, GA
1986 300E 294000 miles
2003 530i
2003 Boxster S