I'm gonna begin this post by stating that I don't do electrical very well. Mechanical stuff I've got no problem with but electrical just doesn't click in my brain.

I'm putting a new (to me) tire carrier on my JKU. The Crawler Conceptz body mounted carrier to be specific. As part of that, I'm relocating my tag to the center of the spare but I also lost my center mounted 3rd brake light. I've looked through the commercially available options out there and for various reasons just don't like 99% of them. As such, I've looked at other options and I'm currently thinking about using a driver's side tail light off of a 1932 Ford. This fixture (shown in the link and the attached pic) is a combo of both brake light and tag light so I kill 2 birds with one stone. However (going back to me and electricity), I'm not sure how to wire this up and since it's got LED circuitry in it, I don't want to short it out and fry the board. The instructions list the following:

BLACK - Tail lights
GREEN - Stop/Turn
HOUSING - Grounded

Now, the harness/pigtail that was running from the tailgate to my old 3rd brake light has 2 wires. I'm assuming one is positive and one is negative, right? Or is one for the lights circuit and one is for stop? If it's the latter, am I correct in assuming that I can hook one to black and one to green. And since there's no guarantee that the carrier is properly grounded, I should then run a ground wire from the housing back to bare metal on the tailgate?

Any help is appreciated.

1932 Ford LED Tail Light Assembly

 

I had no dang clue that '32 Fords had LEDs back then!

The one thing I'm thinking that might cause a problem is that the plate light illumination looks to be tied to the tail lights (running lights). You are wanting only the brake light feature and the plate light, but when you're NOT braking, the taillight should NOT be illuminated. I'm wondering if this might be trickier than you first thought, or maybe I'm wrong.

 

The tag light is included in the "Tail Light" circuit. You want the 3rd light illuminated like your tail lights when your lights are on. It just gets brighter when you hit the brakes.

I asked the same question a few days ago on Speedway's site and it got answered finally but was after I had posted here. They confirmed it can work like I want it. I'm now just curious what the 2 wires in the factory pigtail for the 3rd light actually do. I'm now convinced one is for the taillight circuit and one for brake light circuit. Anyone know which wire is which?

 

The factory light does not illuminate when the headlights are on, only when the brake pedal is pressed. If that is what you want to do, and it sounds like it is, you will probably have to tap the line from the passenger side taillight and run it through the tailgate. The wiring for the factory 3rd light won't supply the "running light" functionality. Unless I am grossly mistaken. I'm guessing that you just want that light working like a normal taillight based on preference/looks.

 

Resharp001 - You're awesome. I went out and plugged the old 3rd light back in and you're right. It's only illuminated when you press the brake pedal. So you're right, I'll have to tap into the passenger side tail light for power in the light circuit and not the just the brake light circuit. Admittedly, I haven't opened up the passenger side, but would you have any idea which wire it is offhand? I'm sure I can figure it out once I open up the panels but just getting ahead of the game.

On a side note, it's evident now that the 2 wires for the factory 3rd light are hot and ground.

 

I don't recall off the top of my head. Should be easy to pinpoint with a voltmeter though. unscrew taillight, unclip the plug, turn headlights on, put one probe on a ground and use the other to search for the pin that is hot. If you can't locate it, I can probably look tonight.

You might just double check that Colorado doesn't have some provision saying you can't run a 3rd brake light illuminated in the same manner as a taillight. IDK, that seems like one of those things that could vary state by state. I would think it's mainly a safety thing.......when dark out and someone behind you sees that 3rd light illuminate where they was nothing but darkness before, it's a lot more noticeable.

 

Best I can tell, there's nothing regarding constant illumination of the 3rd brake light. Heck, I can't even find mention of it in the state traffic and vehicle code. It only states that vehicles produced after 1958 must have at least 2 stop signal lights on the same vertical and horizontal planes. No mention of the CHMSL. Thanks again!

 

I know here in Texas we ours states that IF you have s 3rd light, it has to work, but you are not REQUIRED to have a 3rd light. I scrapped mine, didn't look back. Circle back around and add a pic when you get it done!

 

A little more digging yielded a bit more info:

The "center high mounted stop light (or lamp) (CHMSL) is a federal requirement primarily. Some states have it required explicitly in their code, some have it implied through language relating to "OEM equipment" and some, like Colorado, don't mention it at all.

The CHMSL is addressed in 49 CFR Part 6.1.4.1 and in Table 1 of the same code. It states the CHMSL must be "...steady burning. Must only be activated upon application of the service brakes or may be activated by a device designed to retard the motion of the vehicle." The language is somewhat contradictory but when compared to other lighting regulations, such as clearance lights, it appears to be OK if it burns steady or lights only upon braking. Most importantly, if it burns steady with the lights circuit, it must light up brighter upon application of the brakes (i.e. no different than your other tailights).

Edit: The citation above is wrong. It's actually 49 CFR Part 571.108.S6.1.4.1

 

What they mean by "steady burning" is it must be on steady, and not be flashing, when the brake pedal is depressed. The part that says "Must only be activated upon application of the service brakes or may be activated by a device designed to retard the motion of the vehicle" clearly indicates it cannot be on all the time.