Try bypassing the switch that disables the window when the gate is down.

 

Good thinking. Could you apply 12 volts directly to the motor to raise the window thereby ruling out the motor as a problem?

 

sure could. You can just unplug that switch and put a jumper across the connector. It should be two blue wires from the wiring harness I have sitting on my bench if it is the same between an 87 and 89 power tailgate.

 

I am new to this site and i know that this reply is late. I had the same problem and just to let you know, there is a saftey switch on the drivers side latch mechanism. It has 2 blue wires on it that will not allow the window to go up while the tailgate is open. Mine was loose and it kills power to the up side of the motor. I just took the cover off and wiggled the wires. It worked!!

 

I will definitely check that! Thank you for replying and no it's not late. This problem has still not been solved! I will what that safety that you recommended. I have not been able to try a couple of the tips I received here because the blazer is currently stashed in a building not being ran right now, but I will check into it!

 

It is kinda hard to see but if you reach in there you will feel the connector. I cant remember for sure but i think i put the window up the way you have been doing it and it made it easier to see the connector. That connector acts as a ground for the up portion of the motor. Basically a safety so someone cant role the window up if tailgate is open. I was about to buy a motor until i found that connector.

 

How do you bypass the safety thing, just snip the wires and splice them together orrrr?? Or is it better to leave this in place?

 

It is a good idea to leave this intact. If you need to temporarily bypass the safety switch, you could just disconnect the wiring from the switch and install a jumper wire.

 

Well, that's what it was! Didn't mean to come back so late, but just wanted to say thanks!!

 

The safety switch was the culprit?