Radio Wiring Question

[FLAGG]

I pulled the stock GM AM/FM Tape Deck out of my '86 Sierra last night because it has some bad connections inside (electronic display doesn't work and the left side speaker connections were shot). Anyway, when I pulled out the radio there was the standard 3 pigtails with the four wire connections in the back, but there was one more lone two wire pigtail sticking out of the back of the radio unit. Does anyone know what the 2 wire pigtail is for? The wires coming out of the radio are orange and brown, and I believe the wires on the trucks pigtail were the same color. Thanks in advance.