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1990 K5 rear glass help

The Butcher

The Butcher

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Texas. In a van, down by the river!
Finally took the top off my 1990 K5 to fix the rear glass that wouldn't go down, and I'm puzzled. I have replaced the regulator, the transmission that bolts to the regulator, the cable that goes from the window motor to the transmission, and the inner and outer seals. I have also replaced the window motor with two different (both brand new) motors. It still won't move up or down and both the switch at the dash and the key in the back door will only activate the motor one direction (not sure if it is in or out). It's like there isn't enough power being generated to get the window to move. When I disconnect the cable from the motor and hook a cordless drill to it, I can easily get the window to go up and down even with the drill set at it's lowest torque setting. I thought maybe the new seals might have been binding things up, but it doesn't trip the torque slip on the drill at the low setting, so I don't think it is a friction issue. Is it possible there is insufficient voltage going to the window motor? Also, why would both the dash switch and the key in the back door only get the motor to operate one way (both the same direction)? Any help is appreciated!!!!
 
Check the connections at bottom of gate to body to see is corroded or loose. Make sure you have a good ground. Check the safety switch on drivers side behind latch. If it only goes one way this is the problem. It can be simply bypassed. It keeps the window from going up with the gate open.
 
frankin5 said:
Check the connections at bottom of gate to body to see is corroded or loose. Make sure you have a good ground. Check the safety switch on drivers side behind latch. If it only goes one way this is the problem. It can be simply bypassed. It keeps the window from going up with the gate open.
Click to expand...
^^This.
The ground for the motor is ‘suppose’ to go through the hinges, but if there’s any corrosion or they’re rusty then it makes for a bad ground and lose of power. What you need to do is run a heavy gauge flexible ground wire from the case of the motor, through the tailgate with the rest of the wiring, and to a clean bare metal spot on the frame. Wouldn’t hurt to add a little dielectric grease to those connections too.
 
Also look along the frame and see if you.have any tack welded exhaust hangers. Pretty easy to compromise the insulation doing that. I replaced the wires from the plug at the firewall to the plug at the bumper with 10ga copper. Used the same 10ga to run a new ground from the motor to the frame.
 
Thanks all for the input. It wouldn't surprise me if the hinges are rusted and there is a weak ground, and the safety switch might be messed up. The rear seals on the glass were bad and it let a good amount of water into the tailgate over the years. Hopefully it will be an easy fix.
 
Had a guy come look at the situation and run a new ground. His determination is that the rocker switch at the dash is the culprit. I called a local place that carries 60-87 Chevy parts and they said that switch isn't made new anymore. Anyone have access to a good one?
 
Was the dash switch bad in both direction, did it have power?
 
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Even if the dash switch is bad, does not work at all or has no power. The keyed switch has it's own power supply. They all go back to the main fuse panel under dash. Check fuses.
 
@The Butcher
The window only goes down correct. The gate thinks the window is up with it open. Bad safety switch.
 
That could be part of the problem but when the cable is hooked up to the transmission it won’t actually move the window. The motor clicks but lacks sufficient power to actually move the window.
 
The motor will run it down, but not up right? Yet you can run it up and down with a drill.
 
No, the motor won’t move it either way. Disconnected from the cable the motor will turn, but only in one direction. A drill will move the window up and down without issue even with the drill set at its lowest torque setting.
 
There is a safety switch on the tailgate that will prevent the glass from moving if the gate isn't closed, correct? Is there any kind of switch that prevents the glass from moving if the fiberglass top is not on the truck?
 
Unplug the connection by the power booster. Blue and tan. Jumper 12v straight to the tailgate side of the plug and see if it moves. If it only works in one direction, guessing you lack continuity. If you bypass the safety switch, make sure you keep the blue and tan 3 way to the tailgate switch.

At the firewall plug, put a meter toward the switch side , operate the switch and see if you get voltage. That should prove the switch.

The key switch is separate from the dash switch. It has a red constant 12v, when you turn the key, it grounds one side or another to go up or down. If it only works one direction, I'll bet you have one side open to the motor. If it operates only in the same direction as the dash, again I bet you have an open.

If the insulation is compromized along the frame rail, that could be a cause for not working in one direction.
 
Defective safety switch. Motor will only turn one way and that is down. If the window is down now the glass will not move with the motor connected. if gate is open or down, window will not go up, only down.
 
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