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 right so far, the 4-way connector Wiring FAQ · 16-4B-1 Ford F250 Trailer Wiring Harness Diagram | Free Wiring Diagram Assortment of ford f250 trailer wiring harness diagram. A wiring diagram is a streamlined standard pictorial representation of an electric circuit. It shows the elements of the circuit as simplified forms, and the power and also signal links between the tools.