I just picked up an aluminum cap for my Ranger and I'd like to put a third brake light on it. What's the best way to get brake light power to the light? Tap into one of the rear brake lights, tap into the existing third brake light or is ther another way?

 

I would tap into the third, high mounted brake light. If you used one of the rear lights there is a good chance the high mounted light in your cap would flash when you operated the turn signal from whichever side you tapped into.