The two best suspects are the switch itself and the regulator / motor. We can get a clue if you leave the engine not running, but turn the ignition switch to "run", and turn on the interior lights. Activate the driver's window switch one way, then the other way and watch very closely to see if the lights dim just a little. There's three possibilities. They dim when the switch is pressed both ways. They never dim either way, or they dim when the switch is pressed only one way.
If the lights dim both ways, it indicates current is trying to flow, and it's drawing the battery's voltage down a little, which is normal. This would suggest the switch is okay and the motor is locked up, either due to a defective motor, or, if the regulator uses a series of pulleys and a cable, that cable may be frayed.
If the lights never dim, this also points to the motor. It is not likely the switch is going to fail for both directions at the same time, but the motor can. There is also a thermal circuit breaker built into the motor to protect it from overheating. The contacts on that circuit breaker cause a lot more problems than they prevent. We can identify this as the culprit with a few voltage tests, but you'll have to gain access to the back of the switch, or the motor's electrical connector.
The more common observation is the lights dim when pressing the switch only one way. The switch actually has four sets of contacts, and typically only one set will become arced or pitted first, and that affects operation in only one direction. In this case, if the "up" function still works, the window is up already as far as it can go, so the motor will draw current and try to run, and you'll see the lights dim. If the switch has bad contacts for the "down" position, no current will get through and the lights won't dim.
If you suspect the switch, your best bet is to get a good used one from a salvage yard and pop it in to see if that solves the problem. GM also uses relays built into some of their window switches, especially when it incorporates an "auto-down" feature where you don't have to hold the switch. Those relays are very small with contacts that can just barely handle to current. I have taken some apart to clean the contacts with sandpaper, but given the time and frustration involved, you're better off with a different switch. You can also often find replacements at auto parts stores. They don't normally carry this type of part because there's just way too many different parts to stock them for all makes and models, but when one brand has a common recurring failure, they often have "Problem Solver" display racks with replacements for all kinds of often-needed parts.
If you would like to do some testing before you go looking for parts, it can be done with a digital voltmeter, but it's much faster to use a test light. Here's links to articles about how to use them, if you need them:
https://www.2carpros.com/articles/how-to-use-a-voltmeter
https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester
The voltmeter article shows using an "auto-ranging" meter that selects the best range automatically. If you have the less-expensive meter that you have to pick the range yourself, I can help you set it up and interpret the readings, if needed. I'll look for a wiring diagram and identify the points to test.
Let me know what you find.
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Friday, December 6th, 2019 AT 3:27 PM
