85 gmc 2500 electric window issue

[ashumway6]

hi guys, I've been a stocker on this site since i found it a few months ago. I've always been able to find answers to my problems until this one so i figured i would ask for some help.
heres the problem, my power windows don't work.
when i hook the motors directly to the battery both driver and passenger side motors work.
i replaced both switches even though using a test light and volt meter i can verify that when i move the switch up or down i get power to the up or down wire leading to the motor with 12 volts. however when i hook the switch to the motor i can't get the window to go up or down. I'm at a loss and might be over thinking but i need help.
anything would be helpful.
Thanks in advance

[bake74]

     Did you verify that you had 12 V at the motor with the switch in place and operating ?  It seems like you tested the motor by itself and the switch by itself, but you did not verify that 12 volts was getting to the motor through the switch, you just know the window does not work.
     I am wondering if you have a full 12 volts at the motor running through all the proper circuits.  Maybe you have a drain somewhere in the system, or your motor is just weak enough that anything short of direct connecting to battery is not enough volts.

[bd]

Welcome to the Forum!

Electric window motors receive power and ground through the wire pair (typically brown or tan and dark blue) that connects to each motor.  The motors do not ground through their attachment to the doors.  Verify that each wire pair connected to a motor simultaneously supplies 12 volts on one wire and ground on the mated wire every time the respective window switch is flipped UP or DOWN.  A window motor changes direction (UP or DOWN) when its switch reverses polarity across its respective wire pair. 

Because the Forum is missing the 1985 edition... refer to the 1984 Wiring Manual.  At rest, all wires connected to the window motors are grounded.  When a window switch is flipped UP or DOWN, one of the two wires connected to the motor supplies 12 volts while the other remains grounded.  Effectively, each wire is ground in one window direction, then reverses to become hot in the opposite window direction. 

Since you've already verified that power is reaching each motor on all wires, make sure the ground connection to each motor is complete and functioning as it should.  Your description implies a poor ground connection either through the harness, or between the harness and cab.

Once you've worked out the cause of failure, consider revamping the window harness to incorporate relays for a dramatic improvement in window performance.  See "Wiring up power windows and door locks."

[ashumway6]

thanks for the information it was most helpful,
bake74 i double checked and i was getting 12 volts thought the whole system to the motor.
after much head scratching i finally gave up and started wiring to bypass the factory wiring harness, when i started running the wires through the door jam i found all the wires cracked or broken. so i replaced all the wiring and boom i had windows again and bonus my door locks now work too. amazing how random electrical can be.

[bake74]

     I have always said that electrical if some of the hardest to diagnose, there is just so many things that it can be.