[Wavey]

Steve -

There are 4 types of 3rd brake lights from the factory:

Inside the rear window, mounted at the top.
Inside rear window, mounted at the bottom (may be the same part as the top mounted?)
Mounted flush to the top of the decklid.
Mounted on a stalk at the top of the decklid.

My '88 Carrera has the high inside type and I hate it. It's almost constantly in the way. However it's probably the most effective because of the position.

Good luck with it!