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.

 

[DirtDonk]

Be interested to see what the OP finds.
The ones I'm familiar with are all attached to the body panel directly behind the lamp bucket. Short ground, screwed right to the body.
Sorry I'm not able to grab one of my old housings to see where the ground is attached. I know I have a set or three laying around here somewhere, but almost nothing is easily accessible right at the moment.

Paul

 

[serial car restorer]

Yeah, I'm curious as well. I replaced the lamp buckets in my '69 project, and the entire harness as well. I don't recall any ground wires connected to the original lamp buckets, nor any spare wires back there.

 

[DC_Gearhead]

Sucks because I just tossed my old taillight buckets this last weekend after sitting on the shelf for two years. I can’t remember if they had two wires for the reverse or not. I don’t think so tho.

I’ll dig in more to see where that wire goes. Figured it was just a standard wire and the forum would know right off the bat. Should have know since it’s not shown on any wire diagrams I’ve seen.

I’ll report back with my findings. Paul I’ll look for holes from a ground screw too. Both sides being exactly the same and my wiring being in original condition make the mystery even more interesting.


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[DC_Gearhead]

Ok so here’s what I found:

It is a ground. I checked with an ohm meter. I didn’t feel any places where the ground would attach in the bucket. I pulled off the cloth loom and found it doubles back on itself and is connected to the brown side of the connector (285). I checked and 285 is a ground too which I didn’t realize until now. I assumed all of the wires on the bucket were hot.

Any idea what that female plug is now? It’s a yellow connector if that has any significance.


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[DirtDonk]

So the looped wire with the socket on the end is probably for your license plate light.
Since it looks like it’s coming from the running lamp wire, that would make the most sense. Is yours working?

 

[DirtDonk]

The brown wire is not a ground. It’s simply reading that way because it’s connected to other things that have a ground. Such as the light switch, the light socket that has a ground as long as there is a lightbulb in it.
One place where you can get a direct connection reading with a ohm-meter, would be between the housing for the Backup lamp, and the rest of the housing for the lights.
If they are connected to each other, then the backup lamp should work because it’s grounding through the housing to the body.
If it doesn’t work, make sure you’re getting 12 V to that connection when the back up lamps are activated and the key is in the ON or AC position.

With all that paint, make sure that the screws that hold the housing in place are actually getting a good connection to the metal body. And make sure that upfront, your battery has a good connection directly to the body. And while you’re at it, if you haven’t already, add a ground wire/strap between the back of the engine And firewall.

 

[serial car restorer]

Brown is tail light circuit, and that looped wire is for a side marker. Looks like your rear harness is not original. Must be from a '70 or later.

 

[DC_Gearhead]

So the looped wire with the socket on the end is probably for your license plate light.
Since it looks like it’s coming from the running lamp wire, that would make the most sense. Is yours working?

There was another connector down below that I connected to the license plate light.

Great tip on the “engine to firewall ground”. Two remaining electrical gremlins to figure out……gauges not working and driving lights (in grille) not coming on. Everything worked before I disassembled to paint.


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[DC_Gearhead]

Brown is tail light circuit, and that looped wire is for a side marker. Looks like your rear harness is not original. Must be from a '70 or later.

View attachment 942504

Interesting. That’s kind of what I was wondering. That’s what made logical sense. My Bronco came from my uncle who worked for Ford in Kansas City for 60 years. I would not be surprised if he replaced the wiring with a newer Ford one if he had an issue. He had this Bronco for a long time.

Thanks for the help deciphering my mystery.


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[serial car restorer]

My guess is that while the reverse lights were connected to that other wire, they came on with the tail lights...