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Exterior Trailer Lighting and Brakes


After hooking a trailer up to the tow vehicle, be sure the trailer’s electrical cable is properly connected between the trailer and the tow vehicle and all exterior trailer lights and the electric brakes ( if so equipped) are working correctly before driving away.

Once the trailer’s electrical cable is connected, conduct a lighting check by turning on all the lights to assure they are operational. Turning on the tow vehicle’s headlights should result in the trailer’s running lights coming on. The running lights include tail lights, license plate light, rear clearance and identification lights, and similar lights on the trailer’s front cap, and applicable side marker lights. Test both the left and right turn signals to be sure the turn signals on the trailer are also blinking. Also, step on the tow vehicle’s brake controller in the cab and verify, by slowly driving forward, that the trailer brakes are coming on.

Occasionally, some of the running lights may not work. If you change a light bulb in the non-working fixture and the light still does not come on, the light’s ground may not be making good contact with the metal trailer skin or underlying structure, thus preventing the electrical circuit from being completed. Usually two screws hold the lighting fixture in place. Try tightening the screws. The screws are secured to the metal sidewall skin or structure and sometimes corrosion forms around the screws, breaking contact and keeping the circuit from being completed. Additionally, a white wire in the electrical cable is generally used for the lighting system ground. This white wire must be securely attached to the trailer frame. The cable connector on the tow vehicle’s frame. This white wire ensures the electrical path of return to the vehicle battery, thus completing the circuit between the trailer lights and tow vehicle battery.

Always check that all exterior trailer lights and brakes are working properly before every trip onto the road.

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