I have an 88 IROC, the power mirror switch moves the mirror left and right but not up and down on drivers side, moves mirror in all directions fine on passenger side.
Why does it only partially work? How do I fix it? Thanks!

 

It could be the switch, but it could also be the mirror itself. Try a different switch if you have one available. Mine did something similar when I first got the car on both mirrors. Turned out to be the switch and one mirror for me. The little wires inside were broke on the mirror and the switch was badly corroded.

 

You could always try and take the switch and bezel out of the door and unplug the switch from the plug it's in and check or clean the contacts

 

Check for corrosion in the connector inside the door.

 

A couple of mine over the years have had rust in the electric motors. Some of the motor housings screw together, others are stuck together. In at least one case, I just removed the screws, popped out the motor and gave the gear a twist to break the armature free of the corrosion. After running the electric motor a minute or two, it worked fine until I sold the car 7 years later.

The switches are kind of crap too. To the best of my knowledge when part of the switch dies, the only option is to replace it. From past experience they wont come apart without destroying the switch.

 

Mine do that from lack of use, but after working the mirrors w/ the switch.They eventually "warm up" & work fine.Doubt its the switch if the other side is working fine.

 

Thanks so much for all your help everyone