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Join Date: Jun 2013
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1972 fuse 8 signal fuse blowing brain teaser

Hi
I have reviewed the threads for the forum but this stuff is weird so here goes for your advice.

I have a 1972 targa new to me (and I am still a student of the Porsche world and electrical auto engineering) that has blown the fuse 2 x for the turn signal number 8

The car has issues with the flashers as well that are just plain weird but with the process of logical deduction and a methodical approach I provide this info/riddle.

With fuse in place and "working":

ignition ON ; ebrake on/up for all of these observastions;
the flashers over tach blink both sides as well as indicator light over OEL (should not be); the exterior flashers do not blink.
If turn signal indicator is placed in down/left at this point, then L side only arrow stays on over tach and light above OEL light stays on as well (right side on tach goes off) and outside flasher blinks left only
If signal indicator is moved to right/up then right side stays on dash and over the OEL light as well as right blinker
Now with ignition OFF E brake still up/on following observations;
Adding in emergency flashers turned on it gets weirder...the following observations with the flashers on:
ONLY left flasher goes on on over tach as well as over OEL light stays flashing(something is blocking the function of the right flasher)
Outside of car only left flashers front and rear at this point.
Turning on the left turn signal at stalk and there is no change
HOWEVER turning on the right signal at stalk, there are no indicator lights at all inside over speedo or outside - but all 4 markers are flashing light over the OEL light continues to flash.

When the number 8 fuse is blown or removed the following observations:
ignition ON and ebrake up
the flashers no longer appear on the tach above the OEL indicator
the signals don't work of course

ignition still ON the flashers still only bllink left of the tach and over the OEL light blinks as does only the left indicator outside
moving the turn signal to the left no change and to the right all 4 blink as well as rear brake light does NOT go on on right/passenger (see below what happens when ignition off)

ignition OFF the flashers still only bllink left of the tach and over the OEL light blinks as does only the left indicator outside
moving the turn signal to the left no change and to the right all 4 blink as well as rear brake light goes on -on right /passeneger side!!!

This is so weird
It seems like this is not a simple regulator or ground but a crossed wire(s)

Here is my question .....
other than good luck ....seems like something is crossed into the right side coming from ebrake and tapping into emergency flashers. I will disconnect the e-brake indicator light from the ebrake itself if possible . It may be part of it
The car still blows the fuse when ebrake is off and then that could be a grounding issue I suppose so any advice on how to methodically isolating that?

Any questions that could help solve this mystery
Thanks
Old 09-08-2019, 01:04 PM
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Location: N.C.
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First are you sure the oil light is on? It isn’t the parking brake light?




This is how I would go about fixing this....

First verify each wire is in the correct fuse panel. Google wiring diagrams and you’ll find one for a 1972. A 1971 or 73 might help too if you can’t find a 72 diagram. I’d also consider pulling the instruments and verifying the wires are on the correct terminals.
A wiring diagram will have small numbers written on it. That number should be in the back of the switch or instrument.

Don’t be overwhelmed by the amount of wires. Each gauge has at least 2 wires and bulbs for the brightness.

Then

I’d buy a power probe, or even a simple wire connected to 12v, then go to each fuse and give it power. Have a helper walk around the car and tell you what light is on.
If you have a weird light go on that you weren’t suspecting then that maybe 1 problem.
Make sure all bulbs are in good working order. Corrosion or a wire grounded maybe causing a fuse to blow. There isn’t a single answer I can give you to fix the problem. You’ll just have to sort out by process of elimination.

Couple things to note.
Parking brake is probably the light you think is oil.
If you shut off the car with the left turn signal on. Your left signal lights should illuminate. Even if the car is off. Same for the right side.
Key out of car the parking brake light should be off.
Ignition switch can be the root of many problems. It isn’t hard to remove and check wires. You will need a wiring diagram.

Good luck.
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Old 09-08-2019, 08:06 PM
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Thank you seafeye!
yes- t be clear the light that goes on on the dash is "above" OEL- not the OEL light itself - so yes that should be OK but the light should not be flashing with parking brakes up along with the turn signals flashing with parking brake on.
Yes I agree sorting with a process of elimination -
Seems like multiple of gremlins
Looking to go from simplest to most complex of sorting.
I will heed your advice and keep the group posted if any unusual findings
Old 09-09-2019, 04:26 AM
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The basic diagram for a 1972 911 is here : http://content.us.porsche-clubs.porsche.com/PorscheClubs/klassieke-porsche-911-en-912-club/files/electric_wiring_diagram_1972.pdf
Old 09-09-2019, 06:35 AM
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Thank you both!
I am going to Targa Carolina and have been prepping my car so this went on the back burner
I am still thinking about how I will take it but this helps a lot
Old 09-14-2019, 01:22 PM
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