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chuck21401 · Joined: 20 Feb 2005 Posts: 244 Location: Annapolis, MD

I need some help chasing down a gremlin.

I noticed that the front/rear parking lights as well as the front /rear side marker lights are not working.

The headlights work fine. The turn signals work fine. The hazard lights work.

I have the wiring diagrams from the Haynes manual (and found a scanned version on Pelican Parts). I checked the fuse (14) and it is fine. I replaced the fuse and checked continuity. I'll also cleaned up the contacts but not sure that is the problem.

I've pulled the bulbs and test those in other fixtures, they all work.

I checked the ground at the front of the car near the headlight and in the back near the taillights -both areas are clean and the previous owner had cleaned the contacts and installed a new bolt to ground everything. I believe there is another grounding location behind the fusebox...I need to crawl under the dash to find that one next.

I think the next step would be to check the headlight switch. In looking at the wiring diagram, it looks current flows from the switch to fuse 14 through a grey/black wire. So with the switch on...I should see 12V or so there right? If not, could the switch be bad? It just seems odd that one function of the switch would go bad.

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1981 Porsche 931

Paul · Posted: Thu Apr 30, 2020 10:59 pm Post subject:

With the key out of the ignition and the headlights off, what happens if you activate the turn signals?

This should light the parking lights on the side based on the turn signal lever position.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

chuck21401 · Joined: 20 Feb 2005 Posts: 244 Location: Annapolis, MD

Paul · Posted: Thu Apr 30, 2020 11:49 pm Post subject:

If you don't have 12v at fuse 14 with the parking lights on, it is most likely the headlight switch or a bad connection in or on the fuse box.

Check for 12v at fuse box E1 using a test light.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

chuck21401 · Joined: 20 Feb 2005 Posts: 244 Location: Annapolis, MD

chuck21401 · Joined: 20 Feb 2005 Posts: 244 Location: Annapolis, MD

I removed the steering wheel and stuck my head under the dash today.

I found the grey/black wire at E1...hmmm looks discolored near the plug!

Before going further I put my voltmeter on the back of the plug at E1...12V with the switch on. Checked for voltage at fuse 14...still nothing.

Finally was able to get it unplugged. Melted plastic...discolored pin.

I tested for continuity at the front of the plug....check...but didn't check for 12V yet.

The previous owner installed fog lights; the fogs are wired into the parking lights. There is no relay. So I'm guessing the circuit was overloaded....and meltdown.

In addition to the melted plug/crispy pin...I'm guessing there is a problem inside the fusebox? Ugh.
_________________
1981 Porsche 931

Paul · Posted: Mon May 18, 2020 9:35 am Post subject:

Great job on the pictures.

Do you have continuity from location 1 in the plug to fuse 14?

With the parking lights on confirm you have 12V on E1 in the fuse box. Use a test light not a volt meter.

What size fuse is in 14?

Disconnect the fog lights.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

chuck21401 · Joined: 20 Feb 2005 Posts: 244 Location: Annapolis, MD

Paul · Posted: Tue May 19, 2020 11:43 pm Post subject:

Glad to help. At which point were the fog lights connected? Were they on a switch or always on with the parking lights?
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

chuck21401 · Joined: 20 Feb 2005 Posts: 244 Location: Annapolis, MD

slowcarfast · Joined: 03 Jan 2020 Posts: 18 Location: Seattle, WA

I think it will be easier to just do your own wiring for the proper fog lights and not worry about the factory harness. Just take switching current for the relay from one of the two low beam feeds, through the fog light switch. Then fog lights can be turned on only with low beams on, and switch off automatically when high beams are on. Power to the relay direct from the battery + post. Run new ground wires from each fog light to the factory grounds at the front of the chassis, left and right. The hardest part is just getting all the bits together. Don't forget cable sheathing!
_________________
1981 924 Weissach Ed #187
1971 MG Midget

slowcarfast · Joined: 03 Jan 2020 Posts: 18 Location: Seattle, WA

Oh, and re the switch, I just put a switch for driving lights in the factory fog light switch position. My new switch is a standard size, but larger than the hole provided. Interestingly, it's the same size as the combo seat belt/brake warning lights hole on the other side of the center console. So I just cut the hole for the switch bigger. Understandable if you don't want to alter the console, tho.
_________________
1981 924 Weissach Ed #187
1971 MG Midget

slowcarfast · Joined: 03 Jan 2020 Posts: 18 Location: Seattle, WA

And I'd also love to know if Paul has a theory on how the added fog lights caused this problem. Maybe it's impossible to say, though, without seeing exactly what the PO did to wire them. The fact that (s)he wired them to the parking lights makes you wonder what other bodges they came up with.
_________________
1981 924 Weissach Ed #187
1971 MG Midget

Paul · Posted: Mon May 25, 2020 11:11 pm Post subject:

Hard to say without knowing how they were connected.

One SWAG is that they were wired between E1 and fuse 14 meaning they were not fused. The overload eventually caused enough corrosion/resistance at the fuse box so that the fog lights soaked up all available current leaving nothing for fuse 14 and the parking lights. This could explain why removing the fog lights from the circuit caused the parking lights to work.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

slowcarfast · Joined: 03 Jan 2020 Posts: 18 Location: Seattle, WA

@Paul : I like it. Sounds reasonable to me.
@chuck21401 : Speaking of fuses, of course you would fuse that new high-current feed to your new fog light relay!
_________________
1981 924 Weissach Ed #187
1971 MG Midget