I know there is a write-up floating around somewhere but I thought I’d make one with pics.
1. Get an impala or monte carlo 3rd brake light. Part # 10319332; years 2000-2005.
I bought mine used off ebay but other options are the junkyard, the dealer or gmpartsdirect.com. The ones from gmpartsdirect are around $70.
The impala light will not affect cruise control (it has the required resistance built-in).
2. Take apart the impala brake light and take out the led strip.
To remove the strip press the 2 tabs on back of the brake light bracket. I used an Allen wrench to press them down and the led strip popped right out.
Then pull out the red and black wire.
Optional: Extend the led strip wires. I just had enough length to plug mine in, so add more wire to make it easier on yourself.
3. Take out your stock brake light.
Unplug it and take off the 2 10mm nuts.
Push down on the tab on each side of the housing and pull straight down.
4. Take apart your stock brake light. Separate the chrome reflector, lens, and the black piece with the bulbs. You won’t need the black piece with the bulbs anymore.
5. Attach the led strip to the chrome reflector.
I used 3M double-sided foam tape (the kind you can use outdoors) since I had it on hand. I put 2 pieces on the reflector and on the back of the led strip. Make sure the surface is clean & dry and you press the tape on firmly.
Other options I’ve seen used are super glue, hot glue/hot melt, & double sided tape + zipties.
6. Pull the led strip wires through the hole in the chrome reflector and plug it in to your stock plug.
The stock plug is labeled A and B. Plug the tab on the RED wire into A. Plug the tab on the BLACK wire into B.
If you want you can start-up your car and test the light to make sure it’s working.
7. Wrap the plug in electrical tape & reattach the lens to the housing.
8. Put the brake light back into the trunk and tighten down the 2 10mm nuts.
If you can, push the plug into the chrome reflector so it sits behind the led strip (just for better protection of the plug)