One issue I have with the electrical system is around the turn signal and brake light operation. When I operate the left or right turn signal, the correct front-signal works. However, both rear turn signals operate simultaneously. Furthermore, when I apply the brakes, the brake lights cause the turn signal to freeze.

I start from the front of the truck and checked what was coming out of the two turn signal wires for the rear turn signals from the turn signal switch, since those were easy to disconnect. They appeared fine.

I then decided to crawl under the truck and check out the wiring. What a mess! Some things I found:

• There was an original (well, I assume original) license plate holder with a single bulb mounted behind the aftermarket bumper.
• There is a pair of license plate bulbs on the aftermarket bumper. One was spliced into the wiring, the other wire was cut
• I found that there was some weird splice job that spliced the passenger side turn signal/brake light wire into the driver side.

So this is my problem, and I think it explains both issues. Since both turn signals/brake lights are linked, when either signal is on, the other comes on. When the brake lights are depressed, normally the turn signal interrupts the brake light, but in this case the other un-interrupted brake light “wins” and both brake lights stay on.

Looking more, the wiring is a lot worse than I thought:

• Tracing the 3 wires from the engine compartment (yellow, green, brown), at the first connector under the truck bed, the brown wire had broken off the connector, and some splice that was literally twisted wire and black electrical tape took over
• Following the wires to the driver side tail lights, there is a complete rats nest of wiring, with wires just twisted together and covered in tape. The wires that run to the taillight pigtails are bare wire.
• The factory wire cover (a cloth-like material) seems to be present. The original-looking license plate bulb wire is wired in somehow
• The new license plate bulbs appear to have simply been spliced into the tail light wires.
• Good news is the taillight pigtails are intact; the connectors are up by the taillight housing, not under the truck.

Even though there are only 3 wires at play, I figured it’d be cleaner to purchase a replacement rear tail light harness. However, it is NOT clear who sells the correct one. Furthermore, looks like I need new brake/tail light pigtails.

Tail Light Wiring Harnesses

I’m expecting something like 5 connectors on two parts. See this diagram:

https://www.fordification.info/tech/images/wiring/1965-lighting03.jpg

• 282 – Green passenger side brake/turn signal
• 282 – Yellow/black driver side brake/turn signal
• 285 – Brown tail light

Part 1 – Engine to driver side

• Engine compartment (3 pins – green, yellow, brown)
• Driver side tail light connector (2 pins – yellow, brown)
• Driver side cross-over connector (2 pins – green brown)

Part 2 – Crossover

• Driver side cross-over connector (2 pins – green, brown)
• Passenger side cross-over connector (2 pins – green, brown)

Here are some of the tail light wiring harnesses I’ve found:

Wiring Harness Main To Taillight – 1961-66 Ford Truck Part #: C3TZ-14405-ER

Features:
• Long Bed• Main Harness to Taillight
• Runs along Frame

From the 3 connectors this is clearly limited to running from engine compartment to drive side tail light. So this by itself is insufficient, I’d need the cross-over harness.

Taillight Crossover Harness – 1961-66 Ford Truck Part #: C1TF-13A409-AF

Features:
• Connects Main Harness to Taillight Socket Wiring
• Connects Left taillight to Right taillight
• Exact of Original

This one is called a crossover harness only, but the picture is odd – it seems that it has more than 2 connectors and includes yellow wires. The cross-over from driver to passenger side only needs a brown and green wire.

I emailed Dennis Carpenter to ask if what I needed and they said both of the above. But I wanted to see what this one was first, so I ordered it and will order the other if necessary.

Update

I received this part from Dennis Carpenter. I confirm it is only the crossover harness. For some reason, though, it is more complicated than expected with additional wires and connectors present for taillight/brake light.

The good news is there is, in fact, an additional bullet connector which I assume is wired to the taillight and is present for connecting a license plate bulb. I should be able to wire up something that inserts into the bullet female and splits out to both my license plate bulbs.

So of course this means I do need the other part.

Finally there is this one:

CJ Classic Trucks Taillight Wiring Harness With Taillight Crossover Harness USA Made F-100 1965-1966

Seems to be a combo set. The one on the right looks like the the engine compartment to driver side. The one on the left… actually looks like the Dennis Carpenter cross-over harness.

So looking at it in more detail it does have more than just the green/brown connector. It appears to have a yellow/brown connector, which seems odd. But it also looks like it may have a single bullet connector that might support a license plate light bulb.

OK, so maybe the Dennis Carpenter one I ordered isn’t sufficient. I’ll wait and see though and try to understand better why there appear to be spurious yellow/brown connectors in the cross-over.

Per update, this was accurate. Looks like the CJ kit is really similar to purchasing both Dennis Carpenter sets. And they both come with that license plate female bullet connector and the extra wires in the cross-over.

Brake/Tail Light Pigtails

Since my pigtails appear to be bare wire and secured with electrical tape, I’m going to need new ones. Here are what I think I need:

Taillight Pigtail – 1953-72 Ford Truck Part #: B6C-13410-A

Update

I unscrewed my taillight sockets and found the pigtails and connectors to be in tact, so good news I don’t need the above.

Other Parts

The wires to the taillight pigtails have an attached rubber grommet where they feed through the frame. Looks almost integral to the wiring so cannot be re-used. I ordered new rubber grommets from Dennis Carpenter. They are a different style but look like they will do the job: Taillight Wiring Grommet – 1961-72 Ford Truck

Summary

To be honest, there isn’t much to these wiring harnesses. The biggest issue is plugging into factory connectors. These weatherproof connectors don’t appear to be available – or at least they only come as pigtails. Otherwise I could make my own from about 25 feet of wire.

What is clear – these sites like Dennis Carpenter and CJ – offer very poor descriptions of their parts. You’d think for such a specialized product, manufactured in-house with such limited use-cases, there’d be a far more robust description.