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Lots of folks install an aftermarket tire carrier. Many of these do not address the 3rd brake light that usually gets tossed with the factory spare tire mount. If you fall into that category, then here is an easy project for getting a 3rd brake light back onto your TJ.
If you're not experienced with electrical projects, then this one may be just what you need to get you going. It is not difficult but covers most of the basics for an electrical installation. If you are an electrical newbie, then read on get your parts ready for the install.
I started this project thinking (and taking photos) that I was going to use a 4 wire trailer connector (had it sitting in the electrical odds and ends box) to power my new 3rd brake light. But once I got into the project a bit, I realized that I could not tap the existing brake lights (the left or right LED lamps I installed) to power the 3rd light. Why? Because by the time the brake pedal signal gets to the right or left rear light, it also is controlled by the turn signal flasher. If I used the left brake light, my new 3rd brake light would flash when I was signaling for a left turn. If I used the right brake light as the power source, the 3rd brake light would flash when I was making a right turn.
So....scratch the idea of using the 4 wire trailer connector and pretend it is NOT in the above photograph. But...the 3rd brake light in the photo was used so lets get on with that.
For the 3rd brake light LED, I cheated and used a wheel center cap that already had an LED lamp and mounting grommet installed in it. I got it from Toys by Troy. If you have a wheel center cap, you can pick up a two wire LED lamp assembly with a rubber mounting grommet and make your own. Your choice as to how you want to do it. Although I have a set of center caps that I no longer used on my wheels (which would make an excellent candidate for this project), I was pressed for time this time around and got the ready made unit from Troy.
If you do not have a 12V test light, you need to pick one up at your local auto parts store. Here is some info on how to use it. You could use a multi-meter for this if you have one available. Since I am going to tell you the colors of the wires, I you don't really need a test light or multi-meter. However, I always try to pick up something useful when I do a new project (at least for the first 40 or 50 mods anyway).....that way you accumulate good tools and it doesn't break the bank all at once.
As I mentioned at the start of the write-up, the trailer harness wasn't going to work. The two wires in the above photo were removed from the factory connector (mounted in the back corner of the tub) that the tail gate contacts to power the factory 3rd brake light. Since I had already removed that connector from the tail gate, it was no longer being used in the tub. These two wires were exactly what I needed to power the new brake light. The black wire is ground and the white/tan wire is +12V when the brake pedal is pressed. These are just push on terminals can easily removed by just pulling them off the connector. You access it by opening the plastic fender liner at the passenger rear of the body. When the plastic fender liner is opened, you can reach up inside and pull the wires loose.
You should check the electrical wires that you removed and make sure they are functioning properly. Using your test light, check the white wire while someone pushes your brake pedal (or push it with a block of wood between the pedal and the seat). The white wire should cause your test light to illuminate. Checking the black wire, the test light should not illuminate. You can also clip the test light's ground lead to the black wire (make sure it makes contact inside the rubber boot). Now touch the test light to the white/tan wire. It should illuminate.
With the power source properly identified, it is time to extend the wires on the LED power connector. Mine had two wires, one black, the other white, which is pretty much standard for a two wire LED assembly. The white wire is the LED ground and the black wire is the +12V connection for the LEDs. (why can't they make the ground black like everyone else?)
I stripped the LED power wires back about 3/8" and then got several feet of 16 gauge wire to extend the LED's power leads. I soldered the wires together and insulated them using two pieces of heat shrink tubing. A couple feet of wire loom keeps the wiring together very nicely.
Oops....there is that stupid 4 wire trailer connector.
Pretend it is not there and that a couple of wires are sticking out of the wire
loom. Anyway, you get the idea....enough wiring was added to the LED power
leads so that the power source can be reached.
More 3rd Brake Light