95 Transport Power Window Issues

I am having an issue with my power windows. My vehicle is a 95 Pontiac Transport and both power windows didnt work when I bought it. The previous owner included new power window motors with the purchase and he assured me that replacing the motors would fix the problem. Before I went through all that work I decided to make sure that the motors were indeed the problem. I undid the connector from the old motor and plugged it into the new one and I got nothing. I checked with a test light to see if I was getting power and I even jump wire tested the new motor to make sure it was working. Both worked just fine. Jump wire testing the old motor produced nothing more than a "faint hum" both nothing else. I would really hate to replace both motors on the doors and get nothing to show from it. Is there something i am missing? I have checked the fuse and the circuit breaker. I even checked the plugin for the circuit breaker to see if I was getting 12V and it was, but the connector to the window motor was only getting between 6-7 volts on both wires. Could this be the problem? or is it normal? Any suggestions or ideas would be appreciated. Thanks

Driver switch is a common problem. All current (+12 V AND ground) passes through the driver switch..even if you use the passenger side switch. so check that out first.
Ground bus return has been mentioned in a few cases too.....I think ths ground bus goes through A pillar base and under the driver side floor carpet where splice corrosion has been mentioned....anyway check the driver switch first. THis diagram can help:
www.avigex.ca/xport/pwrwindows.jpg

Thanks for the reply, I forgot to mention that I replaced the drivers side switch thinking that could be the problem too, but still no good. I will check that ground bus and see if that fixes that problem, but would only getting 6 volts at the motor not make the motor work at all?

How do you measure that 6 volt? Between motor connectors?....Try to measure voltage from one side of motor connector to body ground, then other side to body ground...while pressing the window button of course witrh key ON.... One side should be 12v , the other 0 v when pushing DOWN and the opposite when pushing UP. Then on the 0 v side, measure resistance to body ground..should read zero.

NOw if you measure with no load (motor not connected) you might measure some stray voltage even with buttons at rest due to dirt and the like....so you should make the measurments with some load connected ..in fact the best load being the motor itself. 6 volt with no load is meaningless as it can drop to absolute zero as soon as some load is connected.

THe funny thing is you said when you jump test the old motors they barely turn...while the new would work perfectly....please explain....

YOu said "I checked with a test light to see if I was getting power "........well...did you get any...while pressing the window button of course with key ON?

YOU said you checked the breakrs in the convenience center...didn't you?...
www.convenience_center.jpg

Yes I have checked the fuses and the circuit breaker and yes I did have the key on :grinyes: . My test light showed I was getting power at the connector to the motor but when i plugged the new motor in it didnt work. So I used a small 10 amp battery charger to test both motors, the new motor worked like a charm and the old one hummed like maybe it was stuck but it still did something. Could my problem be a bad ground that is tripping the circuit breaker every time I hit the switch? I would think that I would hear at least a little something coming from the motor being the breaker resets itself after 15 seconds. Should I jump wire test the passenger side and see if that side works?

Should I jump wire test the passenger side and see if that side works?

Well....I hate to test a circuit from the end back....but of course you can do that. Check for 12V between contact D and body ground at passenger switch (I was wrong in my former statement: 12V is fed directly to the passenger switch...only the ground side passes back through the driver switch) and a firm 0 ohm to ground on contacts B and F... all this without pressing the driver side button.

I'd rather check separately for the +12v and ground feed at the driver switch (contacts D and B) in the first place....both measured relative to a good body ground.