The main thing is make sure you have a GOOD ground..90% on all trailer lighting probs are grounds..
4 way flat molded connectors allow basic hookup for three lighting functions; right turn signal / stop light (green), left turn signal / stop light (yellow), taillight / license / side marker (brown) and a ground (white).
you can buy one of these at Walmart..any parts store for the GMC. It goes in the wire at back and makes hooking up a snap for the truck. then just match the wires from trailer and your done..