How To Hardwire a New 7-Way Trailer Connector by Function When Wire Colors Do Not Match

Question:

The cable on our horse trailer got caught during a sharp turn and broke right outside the box. It also sheared a wire in the middle. We have patched it so it is usable, but I would like to replace it. The coloring and explanation on this wire does not match our trailer. This one, the blue wire is the brake wire, on our trailer, the blue wire is not used, and it mentions a purple wire, no blue one exists. How would this one have to be wired to match the trailer?

asked by: karin

Expert Reply:

You will need to wire the 7-Way Molded Trailer Wire Connector, # H20046, for function rather than by color. Since the trailer side needs to be replaced, you will need to trace the wires back to see which wire does which function.

An easier option would be to test the connector you have, before replacing it, to see which wire color matches which function on the trailer side of the connector. Using a circuit tester, like # PTW2993, test the trailer side wires for: right turn and stop, left turn and stop, running lights, electric brakes, 12 volt power, ground, and auxiliary (often times, this is reverse lights but is not always used).

With the trailer connected to the tow vehicle, turn on the left blinker. Using the circuit tester, pierce the wires until you find the one that carries a signal in unison with the blinker. Do the same with the right turn signal. Next, turn on the vehicle lights. Find the wire that carries a constant signal when the lights are on. Do not confuse this with the 12 volt wire which will carry a signal even if the lights are off. To find the brake control wire, engage the manual override function on the brake controller. Find the wire that carries a signal when the manual override is engaged. With someone in the tow vehicle and the emergency brake on, put the vehicle in reverse. Find the wire that carries a signal only when the vehicle is in reverse. The remaining wire will be the ground.

Once you have found and labeled all the wire functions on the trailer, you can remove the old harness and install the new one according to the color and functions on the product page:
White = Ground
Red = Left Turn and Brake
Brown = Right Turn and Brake
Green = Tail Lights
Blue = Brake Power
Black = 12 volt (hot lead)
Yellow = Aux