How do you fix dim brake lights in an 1985 Mustang?

dim brake lights are almost always a ground problem. remove the trunk panels on the backside to expose the taillight wiring. there should be some ground wires attached to the body of the car somewhere by the tail panel. the lights are not grounded through the housings (a lot of older cars were). if all else fails, get a multimeter out and determine which color wires are grounds (most likely the black ones), and run your own ground with an inline tap (from radio shack, etc). use a crimp-on ring terminal on the other end of the wire, and either screw it down to the body or use an attatchment nut for the taillight housing for ground. should work... it's not usually a positive power problem.