2. The GM12-R1 harness has four open wires for power hookups. The two red wires are to power any additional audio accessories, but I had no use for them and closed them off with electrical tape. I proceeded to use some quick-disconnect wire terminals I got from a local hardware store to connect the power and ground wires for the interface. The yellow wire was connected to the large orange constant 12-volt power wire on the factory harness. Then the black wire was connected to the black/white ground wire.