I tested the entire harness. I got some bulbs and sockets and had everything hooked up. I made sure my headlight(high and low beams)were working, the horn ,the key switch, the turn signals, I made sure i had power at the coil wires, the brake light, and a couple other things. I just mounted the center of the harness up with cushion clamps. Then stretched every lil branch off and marked it on the board. Then removed the tape off of it.