Back up light wiring to voltage regulator

[Stimorolgum]

Hello

My 911 from late 1973 ( 1973.5) with the CIS engine has a wiring to the voltage regulator going through the back up light.
The connections appear original by looking at it, but I can not figure out why.

The late 1973 had the same wiring harness as earlier 1973 with MFI, and from what I red has some compromises with the wiring.

Any help appreciated

Cheers

/ Martin

[T77911S]

you sure.
I looked at a 73 drawing and it showed power from fuse 8 to the backup switch to the light.
that's it. the drawing was for CIS

[Stimorolgum]

Thanks T77911S.

I saw similar drawing without the funny wiring to the voltage regulator.

[timmy2]

Difficult to comment without seeing/knowing what you are looking at or how your conclusion was made.

[Stimorolgum]

My backup lights don't work so I did some trouble shooting. When opening the 14 pin contact by the 3rd fuse box there was the wire from the gearbox contact to pin number 5 or 6, as the wiring diagram says. But from that same pin ( or female part of the pin) is a soldered wire going to the voltage regulator.
This wire is not showing on the wiring diagram, but looks original.

[T77911S]

you physically traced it back to the VR?

what pin does it goto on the VR

I have seen mistakes on the drawings, so not saying they are correct.


is it possible is it getting power from the VR

[timmy2]

Picture of 14 pin connector showing wires please.
I build these harnesses all the time. Should not be a double wire there.

[Stimorolgum]

Originally Posted by timmy2

Picture of 14 pin connector showing wires please.
I build these harnesses all the time. Should not be a double wire there.

The blue wire comes from the switch on the gearbox and then at the 12 pin on connector splits to continue to the voltage regulator.

[Stimorolgum]

Originally Posted by T77911S

you physically traced it back to the VR?

what pin does it goto on the VR

I have seen mistakes on the drawings, so not saying they are correct.


is it possible is it getting power from the VR

Hello

Yes I physically followed the blue wire to the VR. Can't see any markings on it though to know were on it connects.
I also measured the contact between the VR and gearbox switch and they connect.
I followed the blue cable from VR to nr 12 on 14 pin connector and then continued behind and below the airbox. There seems to be some kind of connector there before it goes through the fire wall?

[timmy2]

Blue wire is correct for VR. And is wired correctly.
Your originally said reverse light wiring on pin 5 or 6 had a double wire.

[timmy2]

Blue wire from VR should go to 14 pin then to alternator. Not behind the air box. Maybe someone spliced a wire into your harness?
Should be green/yellow and grey/brown only to reverse switch.

[timmy2]

Martin,
PM or email me your phone number and a good time to call (with your time zone)
And I can help you troubleshoot on the phone.

[Stimorolgum]

Problem solved

The failure was probably a short circuit in the light cluster.
When the contact to the light bulb is pulled it can bend back and make contact with the metal back plate of the cluster and causing a short circuit.
This caused the wiring to melt.

[timmy2]

Glad you found the problem.

Quite a ways away from the blue VR wiring. How you ended up going down that rabbit hole I don’t know...
Tail light wiring inside the housing was the fault on the reverse light wiring.
For future readers: Unplugging the 6 pin connectors in the trunk to the tail lights is a good way to isolate those circuits to find a fault.

[Stimorolgum]

Yes,I've been trying to figure out what was wrong with the back up light.
The wires to the back up light switch by the gearbox are blue and the other one black, that's why I thought it went to the VR ( same blue color)
But then we saw that the wiring loom was completely cut off and wires changed colors under the isolation tape.
We put battery directly to the grey brown from the 14 pin contact and realised there was a short inside the light cluser.

We suspect that the wiring loom was cut and replaced with a homemade loom due to same short circuit causing wire damage, and then the back up light was left disconnected.

Now I like to clean the wiring up and replace with original colors. Any tips on where to find the wires with these color combinations?