LordHomerCat

iTrader: (2)

I recently bought an 88 TII. Power windows, but the passenger one didn't work and the previous owner said he thought the motor needed replacing. Today I got a new motor, but sadly discovered this was not the problem. I spent the last two hours with my multimeter trying to track down the problem to no avail. Here is what I discovered:

-The motor(s) (old and new) both work fine. When supplied with the proper power they both move up and down as intended.
-The switch appears to work properly. That is, I can measure the proper leads and see the voltage to to +/- 12V as expected. At least, when the motor is not plugged in...
-When I measure the connector where the motor attaches, without the motor plugged in, it looks great. Matches the (working) driver side voltage/amperage almost exactly, goes +/- as expected, everything seems great.
-As soon as I plug something in(a motor, even a light to test with), that's where I am just baffled. Voltage and current drop to zero even when the switch is on. Literally no power is being sent. I know its not the window motor, those are fine. And the switch works properly at no load (or voltmeter only load). But when I put any real load on, even a light with low resistance, voltage and current are both nonexistent.
-The 'Power' switch on the driver side is set to on. And to make sure, I tried both ways, and it didn't work either way.
-What else... All the fuses were fine, none were blown. The window isnt stuck or something (by applying 12V to the motor, I was able to roll it down and then up again). My car has no power issues, and it doesnt suddenly shut off when I hit the switch or something else indicating a massive short.


I am really just out of ideas here. I thought it might be shorted out somehow, but I just don't know where/how at this point given the behavior I have observed. For reference, I am an electrical engineer so I also and pretty confident I didn't misuse my voltmeter and get crappy readings either, although I guess that is a possibility (but still doesnt solve my problem) ? PLEASE any help you can come up with would be great. I am so tired of having one window and a sunroof only. Thanks a lot!

satch

iTrader: (1)

To break it down, The Black/Blue wire at the "passenger switch" needs to have battery voltage. When you press the up button on the "driver side switch" the Red/White wire at the passenger switch should see battery voltage. If it does then it's suppose to pass power onto the Red wire. When you press the down button on the "driver switch" the Green/White wire should then have voltage which is passed through the "passenger switch" onto the Green wire. Which of this is not occuring if any?

ggoldfingerd

iTrader: (1)

It sounds like you have a connection problem somewhere in the circuit. You need to perform voltage drop tests instead of measuring open circuit voltage. This test will show where your power is going. A voltage drop test is usually a better test to do because you're measuring voltage lose due to resistance.

To perform a voltage drop, connect the meter as shown in the picture below. If the wire between R2 and M1 is good, you will see close to 0 volts. If the wire was shorted to ground, you would see a higher voltage. You want to treat your wiring schematic like my circuit, so you will measure from A to B, B to C, C to D, and so forth. Make sure your circuit is in closed loop (fuses in, motor plugged in, etc). You will need to activate the motor while you take the measurements.



Personally, I would start the measurements at the motor. You can quickly check the ground circuit by measuring from the motor connector (-) to the chassis and the positive circuit from the battery + terminal to the motor. You should see close to your battery voltage on one of those circuits. When you do see it, the problem is within that circuit. Then work your way through that circuit to find the exact cause. If your window motor was working correctly, you would see almost all of the voltage across the motor.

If you were truly measuring current at the motor and had 0 Amps (meter is in series with the motor), your problem is before the motor on your wiring schematic. You current reading may have been in the mA or uA range. Your problem could be as simple as a loose ground wire.

Good luck and I hope this helps.

Rob XX 7

iTrader: (8)

if the drivers switch is not operating correctly the passenger window will not work.
I bought a new passenger switch because the old one was giving me problems and cleaning it did nothing- and my window still did not go down

If I put power to the motor and it went up and down. One of my neighbors came over asking what I was doing and I explained it to him and he told me to check the drivers switch, I laughed at him but it turns out he was 100% correct, I put a new drivers switch in and have not had a problem since