brake lights don't work when I press on the brake light pedal

I have a 1991 Chevrolet Cheyenne v6 4.7 liter 5 speed extended cab pick up and my running lights work in the tail light assembly, but the brake lights don't work when I press on the brake light pedal. I replaced the brake light indicator underneath the dashboard that snaps onto the physical brake arm itself underneath dash, I had a shady tree mechanic rewire the wiring for my brake lights underneath the bed of the pick up in the back by the lights themselves. It worked good for a while but now neither brake light lights up ,so I think maybe a wire may have came loose in that back area. could you tell me what color wire that connects to the brakes underneath bed of truck. please e-mail me at lemleyjrjohn@yahoo.com thank you god bless