4 Pin Trailer Wiring Harness Diagram. The white wire is your ground wire. This accounts for three of the colors in the wiring harness.
The white wire is your ground wire. If your vehicle is not equipped with a working trailer wiring harness, there are a number of different solutions to provide the perfect fit for your specific vehicle. As you know the Pilot is pre-wired so the the install is simply a "plug it in" solution.
You can bypass the converter box completely ( I did) and wire up the Hopkins wiring direct I was about to hook up my buddies trailer yesterday when I ran into this problem.
I would suggest printing out the below diagram for reference, and check each fuse and relay as you go.
I drew this crude diagram to help explain. Not sure which wires attach to what on your trailer connectors? It gets complicated when you have trailers with more cables, and in this case, you need an adapter to make the connections.