What are the Wire Functions on a 7-Way Trailer Connector on a 1991 Ford Bronco

Question:

There appears to be a factory installed 7 pole plug w/ a 4-pole plug spliced into it. There are only 6 colored wires going to the factory plug. I cannot locate the black wire from the truck.

asked by: David W

Expert Reply:

It's possible that the trailer connector on your 1991 Ford Bronco was added aftermarket and not all the functions were needed so one was not installed. You can check the functions of the trailer connector using a circuit tester such as # PTW2993 if you do not already have one.

You can follow the diagram I have included here. Ignore the colors and test the pins on the connector for function. That will show you what is present and what is missing. Once we know which function is not present then we can determine what needs to be done to make it work.

If it is the 12-volt circuit you will need about 20 feet of wire # 10-1-1 which is sold in 1-foot increments, and a 40-amp circuit breaker # PK54540. You will attach the 10-1-1 wire to the back of the 7-Way in the 11:00 position. Then route it under the vehicle, avoiding areas that may pinch or burn the wire. Use wire ties to secure it to the vehicle frame or existing harness. Then it will go up into the engine compartment where you will mount the circuit breaker to a bare metal surface near the battery.

Route the wire to the circuit breaker and cut off excess wire. Attach the routed end to the AUX post on the circuit breaker. Then with the remaining wire attach one end to BAT post on the circuit breaker and route the other end to the positive battery terminal.

expert reply by: Michael H