How to Determine Wire Functions of Trailer 7-Way with only 4-Way Wiring Ran for Installing 7-Way

Question:

I have a 2011 Ford F150. I had to replace the 7 point plug on my utility trailer and cant figure out how to connect the wires from the plug so they will connect to the truck. But the wires coming from the trailer has only 4 wires. So not sure what to do now. Like I said my truck has a 7 point plug and the trailer only has 4 wires. So I am really hoping that you can help me

asked by: TIMOTHY S

Expert Reply:

Sounds like your trailer uses a 7-way connector but only has taillight functions carried on the connector so that is why you only have the 4 wires ran to it. What you need to do is determine what each of the wires carries by either tracing the wiring back to the lights or by putting 12 volts on each wire of the circuits with a car battery jumper wire to determine which wires activate each circuit.

Then use the attached diagram to wire it accordingly.

expert reply by: Jameson C