I know this is a known thing, but my rear window will only roll up but not down, this recently just happened. I noticed it started to be a issue when i left the rear wiper on (there is no rear wiper) and didnt notice it till several days later since then i cant roll it down. This is where im at, the window lock is not on, the button makes a click when i press up and down and can be heard at the relay, so there is power to the button and sending signal to the relay. If i sit there and mash the down button like 30 times i can finally get it to roll down and it will work for maybe like 10 mins, anyways im gonna attempt to bypass the wiper safety today, but after that would we suspect the motor? The battery seems good im gonna do a recondition cycle as i do after the winter on all my cars. But maybe some help on other things to check since i have removed the button from suspicion, also the rear lock does the same if i turn it like 30 times it will engage. but u can hear the click.

So i wanted to post what I tried today, after finding out the battery wires were corroded AF i fixed all that, all new terminals, proper wiring and dang my truck fires up quick now, but still no rear window down, I did direct power to the motor and both up and down work fine, I pulled the console switch and saw one of the terminals was a lil corroded, but nothing major and it was on the up wiring anyways, while messing with the switches my dash gauge lights went out, so idk. I can roll up fine, but need to mash the button like 100 times to get to go down, same with the key up works down doesnt, i can see the voltage draw on the battery gauge but only when pressing the up side, down makes the click in the back but no battery draw on gauge. Im a little lost here, if someone can help me determine the next step please

Drivers side B pillar there is "module" 85930-89101 probably relay inside..

Hey, If needed I have one of the modules from an 86. Part # 85930-89101. Let me know if you want it. Mike

Inspect wiring on flex harness between tailgate and body.
If both console and key switches roll window up, and both also cause the relay click but do not consistently roll down, I suspect:
1) One of the wires enclosed in red below is broken. One is Blue-Black, the other Blue-Yellow, OR
2) Relay does not properly switch up and down circuits. To test this, probe pins 1 and 3 for voltage. On UP direction you should get 12V on DOWN direction polarity would reverse (you will read -12V)


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How about using the keyed switch at the tailgate. Does it operate correctly?

Dont forget to make sure the wiper motor is in the parked position.
If not it will prevent window operations.
Mine used to be intermittent due to this issue.
When you mentioned your problems began after operation of rear wiper triggered my memory!