So on my 90 K1500 the passenger side window only goes down. I have removed the motor a direct wired it to 12 volts. The motor works just fine on the bench. I have checked the wiring to the switch and have 12 volts. I have checked the power coming out of the switch and at the motor connection and have 12 volts on both wires. I even checked the power from the drivers side switch to the passenger side and have 12 volts.
Any ideas why the window only goes down?

 

Either the window/linkage is binding and/or needs lubrication or the motor is worn out. The reason it works fine on the bench is because it’s not under load - in the door, going down isn’t really putting it under load, but lifting the window up is.

You can try spray lube on the pivot points of the track and linkage and apply a thin film of lithium grease or Vaseline to the edges of the window and see if that helps, but most likely motor replacement or repair will be the fix.

 

another issue can be you may be able to see 12v at the switch and after but put those volts under some resistance and the volts will disappear. much like a poor connection on the battery will show you 12v but once you try to start it you will loose all power. so your issue could be A. bad motor B. Bad switch or C. Broken wire.

 

Well I tried a new motor and new switch and neither corrected the issue. I also made sure that the window moved free in the track. I have checked the ohms on all the wires and made sure non of them are shorted ground or power. Did I mention that it doesn't matter if it's installed in the door or just plugged into the wires. Still the same thing.

 

See diagram below.

The right window has an external power source to the switch, but up and down both ground through the driver side switch. If the motor and passenger side switch are good, and you have power at the pink wire (verify with test light using a body ground), the only thing left is the path to ground for the up circuit.

With the key on and the passenger switch unplugged, jumper a test light between Pin A (pink wire) and pin B (tan wire). The light should come on. While keeping the test light connected, wiggle test the harness where it passes through the door jamb and the driver side door jamb (a helper will make this much easier). If the light goes out or flickers during the wiggle test, remove and inspect/repair the harness where necessary.

 

Sounds dumb, but have you tried it with the door open and or closed, also, might I recommend checking the grounds, if you have not already done so. P.S. First post on this forum!