Here is my take on your problem:

The portion of the circuit board where the connectors touch is has become faulty, burned, or otherwise messed up.

To check this, you will need to (1) remove the connector, and (2) use a mirror and a flashlight to look at the underside of the part of the circuit board that the connector fits on to. I dunno how to fix burnt spots except for a new circuit board.

Good Luck,

Bob

:>)

I've always had trouble keeping all my taillights functional. The left brake light in the sedans seems to be worst in my experience. I think the spare tire hits it...
Anyway, remove the socket, make sure it's a three-pin socket, and clean the three ears on it with a nail file or fine sandpaper. Clean inside the socket too, if there's white corrosion in there. If the bulb is faulty, replace it. If the glass is cloudy, white, yellowish, or cracked (possibly broken off!) then you're getting water in that taillight. Water collects in the 2 brake light housings of the sedans. The quick solution is to drill a small (1/8" or less) hole in the bottom outer corner of the light- the water then drains out and you get a couple more years out of the light assembly. Long term, the taillight is shot and you need a new one. If it's cracked anywhere, or deformed from bulb heat, it's probably time to consider replacing the whole thing. (You can't buy sections or parts except for the reverse lens, circuit boards, and sockets).
These sometimes take a little fiddling with- try bending the socket's metal ears up for a bit more contact pressure. Also make sure the circuit board is clean- a pencil eraser does nicely. Sometimes rotating the bulb socket back a little makes for better contact.
Clean the ground screw and the spot on the body where it goes- you need shiny metal for good contact.
Also make sure the brake lights do have DIFFERENT sockets left and right. I believe the right one is supposed to be the white one. Can't remember off hand. Either way, one's white, one's black, they're not interchangeable.
IF the third brake light is working, then the circuit has power and the fuse is good, and the brake light switch is good.
Good luck with it!
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Rob Bareiss, New London CT ::: '87 244DL/M47- 225K, 88 744GLE- 209K, 91 244 183K. Also responsible for the care and feeding of: 88 745GLE, 229K, 88 244GL, 146K, 87 244DL, 235K, 88 245DL, 236K

It sounds like you have some real ground issues. Check the ground wires going to the taillights. Also, get a small brass brush, and clean all the bulbs, bulb holders, and the contacts at the pc boards on the lights. Use a little dielectric grease when you reinstall the bulbs.

Bosch electrical systems can be as bas as Lucas when they're not working right.
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1991 245, 61k miles, looking for a 5 speed 92-93 245 cheap.