I have an 89 740 gl with 230k miles on it and before everyone refers me to the bulb failure relay... read on.

So it started when i had my left blinker on and even though it worked... the "light out" warning would signal. Then one day, BAM no radio. When i braked, the radio (aftermarket) would light up. When i turn left, my reverse lights would flash. Turning right, everything was fine. Brake lights worked... i think. So i bought a used relay and radio now works. The left turn signal made the bulb out signal again. but then my roommate told me my brake lights weren't working. So i bought a NEW bulb out relay and now the left turn signal works without turning making the "bulb out" flash, middle brake light doesn't work, one running brake light is out on the right side annnnddddd the radio doesnt work now (same issue).

Any help?!

 

check the rear connectors for the circuit boards for burnage. Also look at the circuit boards for damage.

 

I think you have a problem in the blinker lever itself.What you can do is disconnect this lever and see if your problems dissappear.Just a screw or two and it will be off and then if the problems do vanish then you need to get another from the junkyard.And if it doesnt then you have some earthing problem.You need to find these earthing points and do some cleaning up and oil them.Very common earthing fault is behind the right and left headlight under the hood.Check the batteri minus connection to the engine and the chassi also