Chevrolet Repair: Tranny problem, gauge cluster, electrical problem

Question
I have a 1992 Chevy scottsdale 3/4 ton p/u - 350 ci motor, R-700 tranny. One day, transmission would not shift into high gear, speedometer dead (pegged on 0), and brake light was lit (dimmer than when parking brake applied) on gauge cluster. This went on for a week. For a different reason, had to disconnect battery. Afterward, the problem was gone: shifted fine, speedo worked, no light on cluster. Next day, problem was back: would not shift into high, speedo dead, brake light on. Although the fluid does appear a bit brownish, these symptoms are leading me away from tranny problem towards an electrical problem. Where do I start?

Answer
Definitely a wiring problem. There is a short somewhere. Two places to start is the wiring harness on the transmission itself and trace them all to where they begin, second behind the gauge cluster. You want to look for burned spots or places where the insulation on the wire is rubbed through. Typically if the brake light is on it wont let the transmission into high gear(built in safety so you don't burn it up) if there is a short and the brake light is on your truck thinks it is.