Fuse for driver's side running lights keeps popping

[CarreraS2]

I hate electrical.

87 911. Fuse for the driver's side running lights keeps popping. I don't think there are any other items in that circuit, but I'm horrible at reading the diagrams. See below.

Here's what I've done.

1. Replaced the fuse. Without the ignition on, pulled out the headlight switch. Lights worked for about 10 second before fuse blew.

2. Took the rear lights out of their sockets. Repeated 1. Fuse blew pretty quickly.

3. Took the front lights out of their sockets. Repeated 1. It worked! The rear lights stayed on fine for a couple of minutes.

At that point, I thought I had isolated the problem. But, to be sure, I turned the key to the accessory position. Fuse blew.

4. Took all the lights out. With the key in the off position, I can pull the headlight switch out, and the fuse stays. But I think (not sure if I'm remembering this one accurately) when I turned the ignition on, headlight switch out, no bulbs, the fuse blows!

5. Took out the lights, checked the wiring and sockets the best I could. Didn't see anything wrong there. Checked wiring under the dash, don't see any obvious problems.

Any suggestions?

Here's the diagram, if it helps.

[450knotOffice]

I've got an '84 that was doing some funky things with the parking lights / turn signals and side marker lights.

I finally pulled the headlight out to check the wiring inside the bucket. The wiring for the turn signals/running lights and side marker lights is in the same bundle as the headlights. That bundle comes from the fuse box area, disapears into the inner fender near the headlamp and goes right into the bucket behind the lamp. Three large wires feed the headlight. Three smaller wires attach to quick disconnect union blocks and then run out of the bucket through another hole. These three wires power your turn signal / running lamp and side marker lamp.

I had some loose wires in there that would occasionally touch and cause mayhem with my turn signals, etc. I re-attached the wiring and my problems were solved.

You might want to have a look. Do you know how to get the headlight off? If not, there's one screw at the bottom of the trim ring. Remove it and pull the headlamp off. You may need to coax it a little if the seal behind it is sticking to it.

-Scott

[CarreraS2]

That didn't work. I had the headlights out a couple of weeks ago, so I thought maybe I had not connected it well. But everything looks ok.

I tried it with all the running lights out of their sockets, and the headlight out, too. Fuse pops when I pull the light switch.

But, I think I'm getting somewhere. I noticed that my high/low stalk is working funky. First it would not turn on the high beams when I pushed it forward. Then it would turn on the highs, but the lows didn't work. Jiggling it around, I can get it to work sometimes.

Definately something going on in there. My (poor) reading of the wiring chart suggests to me the running lights circuit also runs through that high/low switch.

So, it looks like at a minimum, I have to replace or fix that switch. Probably should stick some relays in line for the headlights (even though they are stock). Hopefully the problem goes away after that.

Another question: What is the common failure mode for the high/low switch? Can it typically be repaired, or is this usually a replace-only part?

[fintstone]

I'm not sure if I understand which fuse you are blowing. Is it the 5A left side marker fuse or the 8A left headlight high or 8A left headlight low?

[john70t]

Blowing fuses most likely means a direct 12v feed wire shorting to ground. If it was after the circuit load (i.e. the light) everything would work the same.
This could happen with a wire bundle being repeatedly flexed and the insulation breaking and touching bare metal- such as at a door pivot without a grommet. Usually most bare metal grounds are covered in paint though.
Also it could be a connector popping off the back of a bulb and touching ground as it's dangling.
The light switch seems like the prime source though, especially if the stalk-joint has loosened. An SC will not have airbags so it should be an easier fix. Test before assembling.

[CarreraS2]

Fint - it's the 5A left side marker fuse. This one seems to control all the side marker running lights, and the engine compartment light.

John, agree on that analysis. Although one thing was odd. The first fuse that I replace lasted for at least 10 seconds before blowing. In my various fuse replacements, most of the times it doesn't blow immediately. If it were a 12v short to ground, wouldn't it generally blow immediately every time?

One thing for sure, though, is something is going on in my high/low/directionals switch. Now I have no low beams and no high beams. The high beams will go on if I pull the stalk back towards me in the "flash" position, but that's it. At the beginning of the day I had low beams and intermittent high beams, and I've done nothing except jiggle the stalk around. No airbags, so I think I'll pop it out and take a look.

Did I mention I hate electrical?

[john70t]

The last fuse could have taken longer to pop because the connection surfaces had developed a burnt carbon layer from previous times which isolated the electric flow. Same as a battery load tester (I think) which uses a direct-short loop which seperates and connects carbon plates to create a load.

This is an intreging puzzle. I replaced the front bulbs with the higher 80-100watt ones without installing a relay kit and promptly burnt up my turn-signal housing. Hehehe, DOH! I put in the relay and replaced the signal housing, except now only the low beams will work.
Electrics do sux, still too lazy/preocupied to chase after it. At least if the motor is too loud you can turn up the radio

[fintstone]

There are a couple of other connectors you can disconnect to help isolate your problem. One is the round 6-pin in you engine compartment that goes to the rear light. Thje other is the 6-pin round connector under the dash that does to the stalk and plugs into the bulkhead under the dash.

[CarreraS2]

Fint, I unplugged the 6 pin under the dash that goes to the stalk. The fuse wouldn't blow after that. But I checked the fuse with a test lamp, and with the dash 6 pin unplugged, the fuse isn't getting any power at either end. So it's not surprising it won't blow!

I'm not sure if that test is giving me any useful information.

The 6 pin in the engine compartment is a good one. Maybe I'll sacrifice another fuse tomorrow on that one! (But it seems stalk related still).

[CarreraS2]

Update: OK, now I think I can officially delare the cause to be the turn signal switch.

Went out to check it again last night, and the headlights were still dead. However, to my surprise, the running lights were now working! This was a surprise, because I didn't remember putting a new fuse in for the running lights. I checked the fusebox, and sure enough, the fuse spot was empty!

It seems something has broken loose in the switch, and the power that should be going to the headlights is now going to the running lights. Weird.

I also read some posts about changing the T/S switch. I took a good look, and it seems like it should be easier than most make it out to be. The only hard connections look like the ones that go to the light switch. But looking under my dash, it looks like there is a ton of room to simply unscrew the light switch, push it back, and drop it down. We'll see!

[CarreraS2]

Replaced the T/S switch tonight after dinner. It was a lot easier than I feared it my be after my search for threads on T/S replacement.

I studied it in Bentleys, and did some reconn poking around under the dash to visualize the task last night.

Tonight, I put the new switch in. It's just a matter of taking the wheel off, taking the clamshell off, unbolting the switch, and disconnecting and reconnecting the wires. The task is made easy because the wires can be disconnected and reconnected one at a time. No need for diagrams, etc. and no room for error!

Some of the posts I read had people trying to do it without removing the headlight switch. 4 of the wires run from the T/S switch to the headlight switch. To replace those wires with the switch in place would be quite a task! Possible, I suppose, but would seem very, very difficult to me. No room to work.

But popping out the switch is a 5 minute task. Once it's dangling under the dash, of course, it's easy to switch the wires.

All total, 1.5 hours of clean work.

And, best of all, problem fixed!

(In looking at my dead switch, I don't see any burned contacts, missing or broken parts, melted plastic, etc. Visually, it looks just fine).

[450knotOffice]

Good for you!! Glad you solved your problem and look at it this way...you just added a little more knowlege about your car to that brain of yours.

-Scott

[famoroso]

Responding to a thirteen year old thread, because... why not!

In preparation for my 4a departure for Rennsport VI from San Diego, addressing my driver's side running light fuse issue was a priority.

I checked the F&R running light and engine compartment light circuits to no avail. Everything seemed as it should be.

Another issue that I was having is that the yellow wire under the dash / light switch would get alarmingly hot when using my headlights (even if only for a short period).

So, I figured I'd A) wire in a Jwest headlight relay and B) douse the inside of the turnsignal switch with Deoxit electrical contact cleaner.

So far, so good. I drove for hours with the headlights on and, as expected, the yellow wire barely warmed up, and the driver's side running lights remain operational!

Problem solved? It appears so.