Standard Color Code for Wiring Simple 4 Wire Trailer Lighting Standard Color Code for Wiring Simple 4 Wire Trailer Lighting. I have had to mess with trailer wiring for years, once or twice a year anyway, and I just cannot keep the color code right, ect white/ground, brn/ running lights, grn/ right turn, yellow left turn? You have it 4.8/5(92)Brand: DekaWiring FAQ · 16-4B-1 Trailer_Wiring_Color_Code | etrailer Wishbone-style harness features a 4-pole flat trailer-end connector. Ground wire is 3' long. the wishbone design Color coded for simple installation White wire (ground): 16-gauge Yellow wire (left turn and brake): 18-gauge Green wire (right turn and brake): 18-gauge Brown wires (tail lights): 18-gauge. Trailer Connectors. Trailer End Connector.