Blown power window fuse. Why?

[Alex599]

Howdy Pelicans,

I was about to replace my driver's side passenger window switch as I noticed during the PPI that the switch did not actuate the window. When I turned on the ignition to confirm the faulty switch, I noticed that none of the three switches worked. I checked and fuse #21 is blown. Here are my two questions;

Firstly, what is the most likely reason this fuse would have blown?

Secondly, would a faulty fuse be the reason my switch wasn't working? I always thought that a fuse either allowed current through or it didn't. No in between...

The fuse was not blown when I stored the car on Halloween. I start the car once a month in a very cold garage. And now that I think of it, I disconnected the battery to install my LED dash lights.

Thanks for your input,

Alex

[Alex599]

And while I'm at it, I shut the lights and removed the key with the turn indicator in the left position. Is it normal that the indicator lights stay on "solid"?

And.. I don't have a number nine fuse (left signal fuse. Coincidence???

[steely]

There could be several reasons: Motor overload due to age and gummed up window guides; exposed hot on sw accidentally shorted to Gnd, or maybe just maybe something got bumped during recent work in the area (dash lites).

Not that it matters, but I am not sure I understand the timing of your PPI and Halloween. How do you know the fuse wasn't blown exactly on Halloween? To what ckt did you attach the dash LEDs? Did the windows used to work?

[Alex599]

Originally Posted by steely

There could be several reasons: Motor overload due to age and gummed up window guides; exposed hot on sw accidentally shorted to Gnd, or maybe just maybe something got bumped during recent work in the area (dash lites).

Not that it matters, but I am not sure I understand the timing of your PPI and Halloween. How do you know the fuse wasn't blown exactly on Halloween? To what ckt did you attach the dash LEDs? Did the windows used to work?

Timeline:
I PPI'd the car on day of purchasse November 1st. Two switches worked, both windows went up and down.
I stored the car on November 5th, unknown condition of fuse.

To clarify, I replaced dash bulbs with LED "bulbs". No messing around with the circuits.

[wrxnofx]

Originally Posted by Alex599

And while I'm at it, I shut the lights and removed the key with the turn indicator in the left position. Is it normal that the indicator lights stay on "solid"?

This is totally normal and correct. If you turn the signal switch to the right with key off, the right side goes on. In the front I believe the light that lights is the parking light bulb, and not the signal bulb.

I believe the fuse that you're missing is only for the 2nd stage of the front and rear bulbs (i.e. the bright flash of the bulbs when the turn signal is turned on). As to why it's not in there, you'll have to put a new on in (of the correct amperage). If it blows, there is a short to ground somewhere, and then you can begin to troubleshoot. It's possible one of the connections inside the turn signal housing came off and is touching the pot metal housing.

When I got my car, neither of the 2 front parking lights worked. When I removed the lens and took the bulb out, the copper connections were completely full of green corrosion. I used a dremel with a wire wheel and cleaned all the connections up. Reconnected and they have worked great still 4 years later. I guess the point is, these are old cars, so sometimes you have to just roll up your sleeves and dive in to see what the deal is.

[Alex599]

Originally Posted by wrxnofx

This is totally normal and correct. If you turn the signal switch to the right with key off, the right side goes on. In the front I believe the light that lights is the parking light bulb, and not the signal bulb.

I believe the fuse that you're missing is only for the 2nd stage of the front and rear bulbs (i.e. the bright flash of the bulbs when the turn signal is turned on). As to why it's not in there, you'll have to put a new on in (of the correct amperage). If it blows, there is a short to ground somewhere, and then you can begin to troubleshoot. It's possible one of the connections inside the turn signal housing came off and is touching the pot metal housing.

When I got my car, neither of the 2 front parking lights worked. When I removed the lens and took the bulb out, the copper connections were completely full of green corrosion. I used a dremel with a wire wheel and cleaned all the connections up. Reconnected and they have worked great still 4 years later. I guess the point is, these are old cars, so sometimes you have to just roll up your sleeves and dive in to see what the deal is.

Ok, ok. Another thing to consider is that my steering wheel is currently off. I didn't think that this might affect the connections. That's what likely cause the overload no?

And as for having to roll up your sleeves I couldn't agree more. I love working on my Nunelfer! I just wish I had more time, a bigger budget and a better shop!

[steely]

First - Congratulations on getting the car!!

I think that is really fuse #1. the blue 25A on the instrument end of the main fuse block.
It is fed pwr from a dedicated window controller, so it was probably spared by the fuse. The short would have to be on the load side.

Since you have a cab, I am assuming no seat heaters (or sunroof) also on this leg.
That narrows it down to windows, so with pwr disconnected, you could do an ohm check from the fuse load side (fuse removed) to ground and see if the short is still there, then continue by mashing each switch in each position since the power is daisy chained to them.

Failing that - how did the windows work when you got it? If they were pretty strong and constant, you might just try replacing the fuse and give it a try.

If they motors were slow, then you may be loading the motor, and a window guide clean out might be in your future.

Just some ideas, hope this helps.
I didn't look into your lights issues. I don't think the steering col' would affect the windows.

[Alex599]

Originally Posted by steely

First - Congratulations on getting the car!!

I think that is really fuse #1. the blue 25A on the instrument end of the main fuse block.
It is fed pwr from a dedicated window controller, so it was probably spared by the fuse. The short would have to be on the load side.

Since you have a cab, I am assuming no seat heaters (or sunroof) also on this leg.
That narrows it down to windows, so with pwr disconnected, you could do an ohm check from the fuse load side (fuse removed) to ground and see if the short is still there, then continue by mashing each switch in each position since the power is daisy chained to them.

Failing that - how did the windows work when you got it? If they were pretty strong and constant, you might just try replacing the fuse and give it a try.

If they motors were slow, then you may be loading the motor, and a window guide clean out might be in your future.

Just some ideas, hope this helps.
I didn't look into your lights issues. I don't think the steering col' would affect the windows.

Ah, you're a genius Steely! Yes, both windows were labouring to go up and down especially the passenger one. So the motors working overtime to overcome the friction would have created the overload?

[Dpmulvan]

Look in the bottom of your doors and see if you find any parts floating around. Spring pivots have a tendency to break off causing your symptom of laboring window motors.

[steely]

Originally Posted by Alex599

Ah, you're a genius Steely! Yes, both windows were labouring to go up and down especially the passenger one. So the motors working overtime to overcome the friction would have created the overload?

nah, no genius, just another proud owner :-)
Dpmulvan makes a key point about the window regulator spring pivot possibly being broken (reduces ability of mech'l spring to assist motor). Any lube in the regulator tracks/guides may have diminished, gotten dirty or even hard. And any carbon build-up on the switches will contribute a little to the power problem, basically the fuse may have blown when you as the new owner exercised the windows - this has happened to many of us with cars of this age.

Not giving you the brush off, but there are quite a few threads on fixing this when you assess your punch list. "Window regulator" is a good term to use for a search. In the end, I removed and replaced my window regulator pivot with a small bolt, and I cleaned and re-lubed the guides, and replaced the window felt(s). Here are 2 related threads, Wayne has a technical post here as well aimed at motor replacement but see if you can squeeze some miles out of yours first.

Power Window Help :1988 911
Part found inside driver door - What is it?


Good luck!

[porschenut]

Put a new fuse in and test the windows again. If the fuse blows again, you have some troubleshooting to do. If it doesn't, then the condition that caused it to blow the first time is no longer present.

The purpose of the fuse is to protect the circuit, especially the wiring, from melting and starting a car-b-que due to too much current flowing through the circuit. Current is measured in amps (amperes). If you exceed the amperage of the fuse, it blows and prevents damage to the wiring or components. Fuses do not partially fail. They literally melt. They either are perfect and allow current to flow through, or they "blow" which means they melt from the heat of too much current going through them. This breaks the connection at the fuse block. Look closely at the fuses in your car. Some have larger copper conductors than the others. The bigger the copper, the higher the fuse rating. Fuses are always sized according to the gauge of the wiring they are assigned to protect. Smaller wiring, smaller fuse. Bigger wiring, bigger fuse. By far, the most common cause of a fuse blowing is a short to ground. Google "short to ground" if you're not sure what it means. No matter what the cause of the blown fuse, it resulted because current which exceeded the fuse's amp rating tried to pass through it. The fuse did its job and kept the wiring from melting, and your car from going up in flames.

The left (or right) lights staying on is a feature called "Parking Lights", and is a feature in all European cars because of a law requiring cars to have their street side marker lights on when parked on the street at night.

[Alex599]

Thanks DP, Dan and Dave. Very informative. I'll start digging and get to work!

Alex

[DRACO A5OG]

OP,

Do you have power seats? The Window Fuse shares it with the power seats. Sometimes the connector comes loose under the seat and will short out on the seat frame or chassis of the car. Take a peak under both seats.

[steely]

Originally Posted by DRACO A5OG

OP,

Do you have power seats? The Window Fuse shares it with the power seats. Sometimes the connector comes loose under the seat and will short out on the seat frame or chassis of the car. Take a peak under both seats.

great point bro' Jim, I neglected to list them.