I used an LED row of lights glued to a chunk of aluminum bolted to the top of the rear window. It lit up the whole inside of the car, reflecting off the inside of the rear window. I added another piece of aluminum under it, to reflect the light outside. That worked great.
I went to junk yard and checked out 3rd. lights. Settled on a Toyota or Nissan as it was about correct height and angle to match my rear window.about $5
just remember that the 3rd light gets power directly from the brake switch, not thru the turn signal, otherwise the 3rd light will blink with the turn signalsI'm seriously considering doing that. I'll be getting a wire head kit and a ton of wires, I'm sure I could connect a generic connector to the brake wiring harness.
The fun part will be tagging, organizing, And running wires properly. No way I'm going to have a rats nest like some of the cars I looked at before picking up my own!