A third brake light helps brighten up the back too.
I got one like this: http://www.scottlandyardspares.com/light16.htm
There are versions that tie in to indicate turns or hazard.
I mounted it on the underside of the sugar scoop. It's hollow so I tucked the wires inside and snuck them down to the multi pin wire connector for the back harness and picked up the brake light wire.
I'm sure you could get one mounted just inside the decklid opening if you don't have a sugar scoop spoiler.
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