Fuse Blowing! Power Windows

[Hirevtuner]

Hey electrical gods here is my trouble. Working on a 1987 930 slantnose and the #1 fuse keeps poping. This controls the sunroof, power seats and power windows. It's a 1987 so there is a power window control module but the #5 fuse off it is working. Power seats are both working but no sunroof or power windows. If I put a meter on the two points the fuse gos in I get 12.4v and no amps if that helps. As soon as I put a 25amp fuse in it pops. Good mechanically but not the best at electrical if anyone can help.
__________________
1981 930 with 411 rwhp

[zippy_gg]

Someone on this forum suggested that I split the power load from the #1 fuse on my 86 Carrera to prevent just what you are experiencing.
See if you have a spare (unused) fuse location or expand your fuse panel and build a separate circuit.
The fact that your fuse blows right after you install it would indicate a short somewhere.

[steely]

Fuse #5 is not on the load side of the PW relay and is not related. it is really powered from the Ign switch.
power seats run off of fuse # 2.
heated seats run off of fuse #1. aha

If it the fuse pops as soon as installed it is a hard short and not likely due to a tired motor drawing more than the normal share of juice when the button is pressed. This is when some folks like to 'split the load' for old NLA or expensive motors.

With the fuse 1 removed, you should read 0, not the 12 V you got across the fuse block terminals, unless you have a short, and chances are that you do have one.

all bets are off if the wiring was modified.

My hunch is the most often used part - the drivers door power window harness feed thru near the hinge or pw switches to chassis.

You could (with Batt gnd disconnected) remove and inspect the switches for frayed wiring / evidence of a hard short to the chassis in close proximity to the switch (or even fuse block for that matter).

Another suggestion might be to - with the battery gnd disconnected and fuse 1 removed,... Measure and record the lowest (range) resistance reading you get with an ohm meter from the bottom F1 terminal to a clean ground point, and re-check the reading each time you disconnect (isolate) each window motor (pain), the SR motor, and the power lead (L&R) to the seat heater (leave the seat motor power line intact).

A good initial reading might be about 0.5 ohms (a half an ohm). Anything lower is bad. Zero is a dead short.

If it does not change (an increase), then you have a short in the harness or SR or window switches. if it does increase, you may have found your offending circuit. The power window harness passes thru the front of the door - it could be chafed there.


Try not to test by sacrificing a good fuse in the F1 spot, you could stress the PW relay.

excellent problem description btw, although you misspelled electrical geeks.

I hope this helps.
(sleepless in Pa.)

[Hirevtuner]

Thanks Dan for the info...
Another suggestion might be to - with the battery gnd disconnected and fuse 1 removed,... Measure and record the lowest (range) resistance reading you get with an ohm meter from the bottom F1 terminal to a clean ground point, and re-check the reading each time you disconnect (isolate) each window motor (pain), the SR motor, and the power lead (L&R) to the seat heater (leave the seat motor power line intact).

A good initial reading might be about 0.5 ohms (a half an ohm). Anything lower is bad. Zero is a dead short.

So I removed the bat. ground and put the meter on the #1 fuse bottom and ground. Showed 0.0 ohms. Wigled wires and nothing. Removed window switches and nothing. Press the drivers side and pass side window switches and I get 1.6-1.9 ohms if that means anything. The sun roof switch shows only .6 ohms when activated. Power seats are both working fine and I do not have heated seat.
Switched out all window switches with a spare I have and made no difference.
Anyone have thoughts on next step?

[steely]

I have to go scratch my head on this a bit now that I see your post.
I also have to clarify my statement about the 'good initial reading' of 0.5 resistance from fuse #1 bottom terminal to ground - that would be true only if you depressed the all of the buttons - not saying to do that mind you, just that my number was wrong for the condition I gave.

The initial reading should be infinite for a good ckt, 0.0 for a dead short, and ~0.5 if everything was on.

Your readings appear to be sane. The 1.6-1.9 would be equivalent to a 6amp draw, but the SR value of .6 seems a tad low but valid, and it equates to 20 amp - which seems high. I really don't know what is really normal for it.

What has me stumped is the 0.0 reading increases when you depress a switch. That is like saying it is only shorted when everything is off. And turning a switch ON makes the short go away. I have to look and see what in the switch wiring could present that condition. I would have expected no change from off zero even with button pushing.

Did the readings return to (0) zero when you released each button? You did all 3 door window switches?

It'd be a bit easier if I knew the motors were disconnected, but that is too much work.

Let me look at it with this info you gave.

[Hirevtuner]

ok got it fixed.
ended up being a faulty window switch and the spare that I switched out was also faulty. After testing it with a meter I used my back up back up spare. lol

[steely]

awesome! - I was getting ready to post the window switch wiring diagram and ask you to vfy, but you nailed it.

[rafaelmarte]

i have the same problem, i take out all the wires from all switch and reconnect by Color with the manual, and the problem was resolve.

you need the electrical diagram to se the colour of the wires .

good luck