I have a reocurring problem with my drivers side window master switch. My drivers side window will out of the blue during starting, power the window down. It will not come up using the switch. Removed the switch and checked power on the switch terminals withe connector removed. I have constant power on the down terminal. Cycling the switch does nothing. All the other switches work as advertised and only supply power when the switch is activated. This told me my switch was bad. I replaced the master switch assy and haven't had a problem until yesterday. Same exact thing happened yesterday while starting the truck. The window went down on its own. Troubleshot again to a bad switch. Continuous power to the down side of the switch terminal. Has anyone heard of this problem? This will be 3 master switches in a years time!!! Help!

 

You might have a broken wire inside the wire insulation in the harness where the door opens, and it only sometimes makes contact. You'd need to find that wire and test it, then fix or replace the wire.

 

My question is how could a broken or chaffed wire cause the internal switch failing?

 

I think it more likely that the original OEM switch lasted 27 years, and that the replacement switches are more poorly made, failing due to either handling more current than they were really designed for, or due simply to shoddy materials and construction. I haven't pulled up the wiring diagram, but assume that 12V goes to the central pole of the switch, and that it is momentary to the up or down side.

I agree that a lot of failures could be attributed to worn wiring harnesses where they go through the door jamb area, and am wondering if you could also be seeing a short between wires there cause the premature switch failure.

This is one reason I own not one but two trucks with manual door windows - both my 1996 and 2006. I always had bad luck in my younger years with power window failures. I do not think I have yet had to replace a manual window regulator. Funny thing though - I had a 23 year old college student from church hop in my 96 truck to go help move something for an elderly lady from our church, and he couldn't figure out how to get the window down. He had never ever been in a vehicle with manual windows! I had to demonstrate for him...