Well, I stand corrected. Starting in 2002 on some GM truck models, they built the Body Computer into the radio to insure it couldn't be replaced with an aftermarket unit. Along with that, the insane engineers lost all track of common sense when it came to designing electrical circuits. The power window circuits that worked fine for over 70 years now have to include multiple computers. In fact, every window switch is a computer module on 2003 models. In the past, a switch with multiple contacts inside ran a window. Today, the switch sends a signal to the built-in computer circuit, then that computer performs the switching functions and runs the motor, but only if approved by the Body Computer. It is not practical to try to transplant the 2003 Body Computer into your truck because it is part of a team that includes the instrument cluster, the door modules, and the Engine Computer. Those door modules run the power lock motors. Those also used to be real simple and reliable, but no more.
What I would recommend as the first approach is to see if you can find window switches from an older GM truck model that will fit in your door panels, then I'll draw up a diagram for you on how to wire them. Regardless of the year, all power window motors run on 12 volts. We need to find switches that didn't have small relays attached to them. That way the internal contacts will be large enough to handle the current directly.
If that is not an option, there is a three-position, center-off, spring-loaded switch listed on eBay that is perfect for this application, but I'll have to check if it will handle the current. You'd have to cut about a 1 1/4" square hole in the door panel, and have about two inches of clearance behind it. That switch will also work for the power locks.
When you're in the salvage yard, harvest the rubber accordion boots the wires run in between the door hinges. Also look for a 30-amp thermal circuit breaker in an under-hood fuse box. Because windows are considered a safety system, fuses are not used because if an intermittent short occurs, a blown fuse is permanent. Thermal circuit breakers reset automatically after a few seconds, so in an emergency, it's possible for the windows to work again.
It's a good idea to use a circuit breaker for the power door locks too. GM used to be good about placing accessory 12-volt terminals in their fuse boxes for add-ons, but they really aren't meant for circuits that draw a lot of current. It's better to run the fused wire right to the circuit already in the fuse box for power windows. We might have to rob the terminals out of a fuse box in the salvage yard. To save a few pennies, they might have been left off on the assembly line since that wasn't an installed option on your truck.
The web site we use for online service manuals is running frustratingly slow today so I can't look at wiring diagrams for earlier years. I'm going to have to dump this on you for now to check in the salvage yards to see if you can find switches that will pop into your door panels. Start with the 2001 models. I'll let you know when I find some years that will work.
Saturday, December 7th, 2019 AT 2:47 PM