Tail lamp wire bushing T-6409 dimensions

[Eric Sole]

The rubber grommets used to make the tail lamp wire bushings dried up and fell apart after thirty-some years of service, so I replaced them with new ones of about the same size.

A local Model T buddy found some old porcelain insulators and we are trying to find out what size the original Ford issued "bushing" measured. I read somewhere that it was made of porcelain, but I have never seen a picture of one.

If anyone has an original of this part, could you share a picture and these measurements?
-Overall diameter
-Outside "waist" diameter
-Inside hole diameter
-Thickness

Detail of the T-6409 assembly (wire and the alleged porcelain "bushing":

taken from the wiring diagram:

Thanks for any information you can provide.

[Cody]

I know it's not super helpful, but I have a copy of the T-6409 engineering drawing (dated 11-25-25). It does not give any information about the bushing, other than it is part number T-4082. For the wire (T-6410), there are three pieces of information: 1, there is one complete twist of the wire at the base of the bushing. 2, the legs are parallel and are 1/4" apart (I assume that this only matters before it's installed onto the car). 3, where the legs start from the twist and bend to be 1/4" apart it is bent at a 1/16" radius (again not sure how important this is after it's installed onto the car).

[Eric Sole]

The piece in the picture is of my doing. I didn't make the wires parallel with a 1/4" between them, they came from the vendor that way and now I know that was factory correct. Having the wire flat below the bushing does make the installation easier as it allows the bushing to set closer to the frame making it more stable. It looks like I gave the wire 2 twists as well, so there are a couple improvements to be made there. Thanks for that info Cody.

[Original Smith]

Looks like you are on the right track!

[DanTreace]

Here's one original tail lamp wire bushing and wire twist in my stash. It's rather stiff now after 100yrs or so, but was probably a hard rubber like material same as the panel plug on the touring cars to fill the hole in the rear body for removal of top prop iron shafts.


The dimensions were hard to determine, best guess is hole for wire is 1/4" dia. And the outer dia. of the circle wire is 1/2".

The wire is .062" dia. The grommet has an obvious groove in the grommet for the wire wrap, and the sides of the grommet are rather conical too.

The wire shows the single twist as noted.

[Eric Sole]

Dan, those images surpass 1000 words. Thanks so much.

Your description of the material reminds me of the conical-shaped rubber grommets used on old electrical appliances which break easily and crumble if you manipulate them too much. They almost seemed to be made of a tar-like material the way they would break up.

I don't know where I came up with the idea of porcelain insulators for the tail light wire. Bruce McCalley's Encyclopedia has only one entry for the word "porcelains", referring to the coil box, and I have yet to glean through my paper copy of "From Here To Obscurity", but it appears safe to say that the T-4082 was not made of porcelain but from a rubber material.

If anyone has evidence of the contrary, please chime in.

[Eric Sole]

Here is my interpretation and how I have fitted the insulating supports for the tail light wire on my 27 Roadster.
The extra wiring loom carries the turn indicator and brake light wires.
I attached the tail light wire separately just because that's how it came from the factory. What can I say, I'm a futz with this kind of thing. Some people enjoy finding all the parts to assemble a jigsaw puzzle, I like finding all the parts to assemble a Model T.