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Third Brake Light not working

After looking at every forum entry I could find (even on different websites - yikes!!!), I have no other recourse than to send my own query out to the community so apologies if this has been covered elsewhere.
I am the proud owner of a beautiful 1986 930 and have recently noticed that the third brake light on my baby no longer works. Obviously, I would like to avoid at all cost being rear ended and want to make sure I am as visible as possible but have not been able to find the culprit (bulb and fuse are working fine). Is there anyone out there who has run through the same issue and found a fix to this annoyance? An electrical diagram/schematic would be very helpful (the links I found on this site are not going anywhere)!
I guess it is important to note that I have the window type and not the "robot kind":

Last edited by eleblond; 09-07-2018 at 12:21 PM.. Reason: Picture did not load
Old 09-07-2018, 11:30 AM
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Old 09-07-2018, 12:40 PM
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Check to make sure the contacts on the housing are fully seating on the metal contact on the glass.

My buddy has a LE last of the G50 3.2's and his light is on the bottom like my modded 85. His contacts were not making contact due to heat and UV warping the housing, causing it not to make a full contact with the circuit.

We bent out the contact so it will fully seat, now he has proper working 3rd brake light.

Btw, Beautiful 930 :-D
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'85 Carrera Targa
Factory Marble Grey/Black * Turbo Tail * 930 Steering Wheel* Sport Seats * 17" Fuchs (r) * 3.4 * 964 Cams * 915 * LSD * Factory SS * Turbo Tie Rods * Bilsteins * Euro Pre-Muff * SW Chip on 4K DME * NGK * Sienes GSK * Targa Body Brace
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Last edited by DRACO A5OG; 09-07-2018 at 08:07 PM..
Old 09-07-2018, 08:05 PM
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Thanks but the connectors are on the brake light itself and the problem seems to be coming from somewhere before the brake light
Old 09-08-2018, 02:02 PM
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Old 09-08-2018, 02:08 PM
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Is there power at these contact, when brake pedal is pressed and the two sides turn on?

If so then locate the tap on the driver side to see if it severed or if the ground side is corroded.

Black with yellow is from left brake light, brown is to ground to chassis


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Originally Posted by eleblond View Post
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'85 Carrera Targa
Factory Marble Grey/Black * Turbo Tail * 930 Steering Wheel* Sport Seats * 17" Fuchs (r) * 3.4 * 964 Cams * 915 * LSD * Factory SS * Turbo Tie Rods * Bilsteins * Euro Pre-Muff * SW Chip on 4K DME * NGK * Sienes GSK * Targa Body Brace
PCA/POC
Old 09-08-2018, 03:01 PM
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No juice but thanks for the wires identification, this narrows down things.
Old 09-09-2018, 06:40 AM
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Circuit.


^^^^^
Here is the HI-RES circuit from the factory manual.

pm me as needed.

Gerry
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Old 09-09-2018, 07:18 AM
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Try this test, connect your volt meter to the black yellow and other lead to a good clean ground while brake is pressed, car in on position.

You should get voltage. If not then, that line is severed.

To check ground, find a hot 12 volt source and connect the leads of volt meter to the brown wire, your should get voltage, if not then ground side is severed/disconnected.

Hope this makes sense?

Jim
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'85 Carrera Targa
Factory Marble Grey/Black * Turbo Tail * 930 Steering Wheel* Sport Seats * 17" Fuchs (r) * 3.4 * 964 Cams * 915 * LSD * Factory SS * Turbo Tie Rods * Bilsteins * Euro Pre-Muff * SW Chip on 4K DME * NGK * Sienes GSK * Targa Body Brace
PCA/POC
Old 09-09-2018, 10:13 AM
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Thanks for the diagram, this helps a lot! The line must be severed somewhere between the 3rd brake light and the left tail light assembly since both left and right brake lights work as they should.
Old 09-09-2018, 01:06 PM
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Light.

Or perhaps a corroded connector issue.

G
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Per Road and Track magazine:
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In the window of a bar in Hermosa Beach, California.
"Happy Hour prices during all car chases."
Old 09-09-2018, 02:33 PM
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Thanks for your help guys, I figured it out and it was much simpler than expected. It turned out to be that the 3-way connector that feeds the 3rd brake light was not connected and the cable it should have been connected to was connected to another, very similar 3-way connector (they must have made a mistake at the shop when I last took it there). You gave me an idea where to look and what to look for. Now to find out what that now-loose 3-way connector function is... Maybe a remnant from a defunct A/C component?
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or European Rear Fog Lights
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'85 Carrera Targa
Factory Marble Grey/Black * Turbo Tail * 930 Steering Wheel* Sport Seats * 17" Fuchs (r) * 3.4 * 964 Cams * 915 * LSD * Factory SS * Turbo Tie Rods * Bilsteins * Euro Pre-Muff * SW Chip on 4K DME * NGK * Sienes GSK * Targa Body Brace
PCA/POC
Old 09-09-2018, 03:28 PM
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Interesting... The wiring would be there already?
Old 09-09-2018, 03:54 PM
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Yes, we all have it.

What color are they?
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'85 Carrera Targa
Factory Marble Grey/Black * Turbo Tail * 930 Steering Wheel* Sport Seats * 17" Fuchs (r) * 3.4 * 964 Cams * 915 * LSD * Factory SS * Turbo Tie Rods * Bilsteins * Euro Pre-Muff * SW Chip on 4K DME * NGK * Sienes GSK * Targa Body Brace
PCA/POC
Old 09-09-2018, 04:10 PM
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The wires are covered by an intact sheath.
Old 09-10-2018, 05:44 AM
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