weird power window fuse issue

[rycar550]

Hey guys,

I am having an issue where I am blowing a ton of power window fuses (fuse 17?). Sometimes it happens when I use a window switch, other times, the fuse will blow the minute I turn the ignition on. Which is weird to me, because I would think that it would not be drawing power at this point. The circuit breaker in the cabin is not tripping. In fact, I have replaced it, and the problem still remains.

Not sure how to start the troubleshooting process here. Any suggestions?

Thanks!
Ryan
1991 318i

[billybobjoseph]

If you have a good multi meter pull the #17 fuse. Turn the key to the on position. Us the volt meter to figure out which fuse plug ( side of the fuse ) the power is coming from. Turn the key off and disconnect the negative then the positive battery lead. Switch your meter to measure ohms. Put your positive lead to the other fuse plug ( where power was not coming from) and the negative to ground. If the resistance is less than infinite you have a short. Pull the window switches and the window safety switch. Pull the green wire with a grey tracer off a switch and retest from the fuse plug with the ohm meter. If the short is still there plug that wire back in and pull the next wire ( same color ) off the next switch and retest. Do this till the short goes away. That's the window circuit with the short. Pull the other two wires from the switch that aren't brown and remember where they go. Use the ohm meter to test those two wires. If there's a short in either or both of them the short is in that wire or the window motor. If the wires both have infinite resistance the short is in the switch.

[jlevie]

My first suspicion would be that there's a frayed wire in the window motor circuit.

[rycar550]

Billybobjoseph - thanks for the input. I will try that.

Jlevie - good point. But would a frayed wire at the motor cause the fuse to blow even when not pressing the window switch?

[billybobjoseph]

Probably not rycar because the motors are grounded through the switch. But you could have both a faulty switch and a frayed wire. Also I failed to point out that you could have a short ( frayed wire or what have you ) in the wiring between the fuse and the switches. You can test with you ohm meter by unplugging all the green wires with grey tracers from all the switches ( remember the safety switch ) and testing from the fuse again.

[rycar550]

Billybobjoseph - makes sense and I will test. Am I correct in saying that no power should be drawn unless a switch is pressed? I just want to make sure there is no other variables here. I guess if the lights are on, then it would pull power, but other than that it should not...correct?

Ryan

[billybobjoseph]

That is correct, the switches ground the motor and supply power to the motor as well. The polarity on the motor changes depending on if you hit the down or up button. Are you having a power drain when you park it overnight?

[rycar550]

no power drain experienced...

[billybobjoseph]

Go to http://www.diakom.ru/CARS2/index.html select BMW from menu on left. Then select the first Russian phrase on the right.Then select third Russian phrase below that ( says Mitchell next to it). In drop down box select year, next drop down box select model, third drop down box select wiring diagrams.

[billybobjoseph]

If you don't have a power drain then the short, if that is the problem, is probably after the switch in the circuit as jlevie said. The only way to know is test it with your ohm meter.