This has been posted on here before at some point. Did the swap last night and it works great.

1 Purchase red LED strip off of eBay for $10, item 320457987472, seller LED-DNA.

2 Remove and disassemble light assembly. Getting the fixture apart is a long process and takes a lot of heat. I used a good hair dryer. If I ever do one again I'm going to preheat the whole thing in an oven.

3 Swap out stupid neon tubes for LED strip. You can attach it to the existing reflector with the adhesive of your choice. It fits snug on each end, make sure it's lined up nice an straight across the reflector.

4 Reassemble light fixture with RTV adhesive sealant. I used zip ties to hold it together for about 3 hours while the RTV cured.

Total cost, about $20, significantly less than a new light (-:

5 Put it back on the car and admire your work. Looks nice, 1cm spacing of the LED's looks stock, like other Caddies with LED 3rd brake light. Brightness is just right, just a little brighter than the LED bulbs I have in my regular brake lights.