W8TVI
Full Access Member
I did this with my '04 Monte Carlo.
Like our NBS trucks, the bottom light was parking and brake light, and the top light was just the turn signal.
To do this mod, you need a test light or multi meter with sharp probes, some weather proof butt connectors (for the new harness), electrical tape, and some inline wire taps.
If you are doing this on stock lights, you will need to change the color of the turn signal lens red some how.
You can get aftermarket tails for pretty cheap that have red in both positions, and would improve the look of the truck.
If you buy the plug from the link above, you can follow these colors, but they won't be the same if you get the part from a junk yard.
To find the parking light wire, turn your parking lights on and use your meter or test light to find the wire (on the brake light harness) that lights up your test light with the parking lights on (double check and turn off the parking lights to make sure you found the right wire).
You will be cutting off the turn signal plug from the truck, and installing your new plug in it's place.
If you use the above plug, the wires from the turn signal go to the green wire for ground (should be black on the truck) and the purple wire for the positive. Verify your wires using your test light again by turning on the hazard lights and probing the turn signal wires until you find the one that flashes your test lamp when you touch it. This is the positive wire (the one that goes to the purple wire on the plug above).
If you get the plug off of a NBS800 truck in the junk yard, you can compare it to the brake light plug on the truck and put the negative to the negative (on my 2000 GMC Yukon XL, it was marked on the plug itself as "G". 1 was the brake light, and 2 was the parking light), and then you can (using the wire tap) tee into the parking light wire you found before to the same wire position on the junkyard plug. Then you just wire the turn signal wire to the remaining wire.
If you are using the plug above, the parking light will go to the yellow wire from parking light wire you found in the brake light harness.
Now check out your wiring job and see if the lights work the way they should by turning on the hazards and parking lights.
If it works, you just need to tape up really well the place where you teed into the parking light plug (if you have dielectric grease, use it here), then use a lighter to shrink the heat shrink on the weatherproof butt connectors.
