This how to will show you how to add a 3rd light to your tail lights (see pics below):
Phillips Screw Driver
Flathead (or something for prying)
18 - 16 Gauge Wire (I purchased 100ft of red 16 gauge)
18 - 16 Gauge(blue) Wire Taps
Wire Clothes Hanger (or something thin and long to run wire through ceiling)
First things first:
To clear up any confusion that may come with this how to, the harness I used was only a 2 wire harness. I was unable to use the harness I had out of another ranger due to incompatibility with the tail lights (without modding the tail light housing). Therefore, my 3rd light was only able to perform one function, which I decided to make the braking light (no blinker). If you were to use a harness from a ranger (has 3 wires) you could have 2 functions (i.e., brake, running light).
Originally I wanted to add the third light to be a brake light and a running light, but as stated above, I was unable to do so with the tail lights I purchased. I thought long and hard about which I'd rather have: running light or brake light. Finally I decided I would go with the more difficult route and make it solely a brake light (no blinker).
Looking at the harness you will see the 3 wires, Black, Brown, & Green/Orange.
Black = Ground
= Running Light
= Brake & Blinker
You can tap into either the Brown and/or the Green/Orange wire and be done. If you would light to make it be just a brake light, your in for more fun.
Make it brake!
Now for the fun part.
First remove the third brake light, then get into the cab and remove the overhead dome light.
Run your 18 - 16 gauge wire FROM the dome light and out through the 3rd brake light hole, trust me it will save you the aggravation if you are using a spool of wire.
Looking at the 3rd brake light you'll see 2 wires; blue and green. You will need to tap into the Green one.
You can reattach the 3rd brake light at this time.
Now you will want to approximate how much wire you are going to need, then give yourself an extra 4 feet on top of that (better to have more than not enough) and cut it off of the spool.
Next we will begin running the wire through the ceiling. Unscrew the plastic hanger hook if you have one, grab your clothes hanger, affix the wire to it and start pushing through the ceiling towards the drivers side of the cab.
Also it helps if you pull out those flat plastic things holding the trim on the B post (next to the seatbelt) so that you can feed the wire down towards the floor.
Now you'll need to pull the trim up from the floor on the driver's side. The screws may be rusted or filled with mud, so be prepared. I had to use a pick to clean out the screws.
Pull up your carpet/vinyl flooring and you will see a little rubber gasket. Poke a hole in it just big enough for the wire to fit snug.
Time to get under the truck, this is where a creeper comes in handy as you'll be working your way down the frame of the truck.
Pull all of the wire through, clean it up, and replace the trim. Start feeding the wire towards the frame, theres plenty of holes. From here just run the wire down the frame towards the tail light.
Now you'll need to take the brake light harness and cut away some of the plastic tubing to access the wires.
Get your new harness and tap the negative to the negative on the brake light like the picture below.
Now tap the positive to the positive of the 3rd brake light wire that you just ran up.
Next you will need to run another 4ft to the other tail light. Tap it into the positive lead before you run it.
Repeat the previous steps for the next light and wrap all of your taps with wire tape.
Congrats, you're done! If you have any questions feel free to PM me.