I am having an issue with my driver side mirror. The mirror will adjust up and down but will not adjust right and left. I disconnected the six pin barrel plug and removed the mirror motor and both of the motors function correctly when voltage is applied (also when polarity is reversed). I removed the Mirror switch and appears to be functional in all directions. I have page 6 of the 87 928s wiring diagram but it doesn't seem to help because of my wiring diagram illiteracy (I am a machinist, mechanical DWG's no problem). However when I tried to check continuity from the changeover switch plug to the barrel plug at the mirror, i find that the first 2 wires (a green and a blue), when checked will each show some continuity to two of the same pins on the mirrors barrel plug. The passenger mirror works fine.

 

Both times I’ve had mirror issues the problem was the right/left selector switch.
Flush some contact cleaner into the switch and work it back and forth. Might fix it temporarily.

 

Thanks, I will try that . maybe some Deoxit 100.

 

So I did a bunch of OHMing and found that the blue/white wire from the changeover switch did not have continuity. pulled the mirror of and fished the wires up through the hole and found that the someone had been in there and did some outstanding wiring. I Love those crimps (Sarcasm). So I stripped fresh wire, soldered and heat shrunk them. Thank you for everyone's reply.

 

The harness in the door bends everytime you open and close it. You may have more wires ready to break or will soon. Pull the card and get pre-emptive on that.

Also, replace the side-to-side ad 4-way mirror switches while you still can. They die internally at age 25-30, seem to be the peak of the curve. Time after that is simply a gift.

These could double in price or to EOA anytime..like anything else that WILL fail that you dont have an eye on.

 

Thank you very much. This is good to know.