Third brake light

[mrmoose]

Ok so my car has a carbon hatch with no third brake light, not even a space for it on there. Soooo I went and bought an led brake light strip to put in the back window so I'll pass inspection. Now I spliced it onto the harness and nothing... Tried runnin a diff ground and so on. I pull out the old multimeter and test the wires. Sure enough when the pedal is pressed there was power. But it only has approx 10.5v it should be around 12 correct? Any thoughs what could be draining the power? Thanks!