68 extra tail light wire?

[DC_Gearhead]

I was out test driving my rig and noticed my reverse lights weren’t working. Popped the taillight off with the volt meter (and rig in reverse). I saw there are two pigtails in the bucket and I had plugged into the wrong one on both sides. What is the other one for? Both are just empty. Everything seems to work.

Original wiring, 1968 so no side lights, single gas tank, no trailer wiring.

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[serial car restorer]

What colors are the unused wires? On the left side, black/red is the reverse lights, brown is tail lights and yellow/black is left brake. (Same on the right side except the brake is green.)

 

[DirtDonk]

Where is your dedicated ground for the Backup lamp bulb? Could that be what the other one is?
I think later models just where the wire without a connector. Right from the housing to the body.
Can you follow that other wire along and check it? With everything off, does it check as a ground?

 

[DC_Gearhead]

What colors are the unused wires? On the left side, black/red is the reverse lights, brown is tail lights and yellow/black is left brake. (Same on the right side except the brake is green.)

That’s what’s connected now. But I have an extra wire. I couldn’t see the color on it with grime and overspray. I’ll clean it up tonight and check.


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[DC_Gearhead]

Where is your dedicated ground for the Backup lamp bulb? Could that be what the other one is?
I think later models just where the wire without a connector. Right from the housing to the body.
Can you follow that other wire along and check it? With everything off, does it check as a ground?

I saw a vague reference to that ground wire in another thread. I did check it last night with the reverse lights on and it was grounded on the driver side. I’ll turn it all off and check both wires tonight.

Makes sense. I don’t have a ground to my taillight housing so they only work once I screw in one of the mounting screws. If it is a ground what should it be connected to, just the body with a grounding screw?


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[serial car restorer]

My '69 did not have a ground wire to the rear light housings.

 

[DirtDonk]

I wonder when they added it?
Maybe it was a later thing due to grounding issues. But I always thought it was a 67 and later item. My 71 has them. Couple of friends had ‘70 models, but I don’t remember ever being inside the tail light buckets.
It was for the back up lamps only, as the backup lamp housing was a later add-on to the overall tail light housing, and was Insulated from the main housing by a gasket. Necessitating its own ground be needed.
Pretty sure the bulb socket only has one wire, and if you look at the replacement housings, they have a push in “bullet” connector that seems to match your harnesses’ empty socket.

Maybe someone with an early model has their housing out and can give us some comparisons.

 

[serial car restorer]

It would be very unusual if the power and an additional ground wire both had the same connectors. The power to a given light (or whatever) is normally one gender, and the ground is the other. This prevents connecting them backwards and having a dead short.

 

[DirtDonk]

And since it’s a female, it would normally be appropriate for power.
But since the lamp bucket has a male connector on it, maybe they did this one a little backwards.

 

[serial car restorer]

Easy enough to put an ohmmeter on that wire and check to see if it is a ground.