Got any diagrams? Pics?I built one for the trailer end with a 4 and 7 pin plug. It has a box with 6 switches, one for each function. It gets it power from a 20' long power lead with a cigarette lighter plug on the end.
For the truck end I made one with a 4 pin and 7 pin plug and a 20 foot lead running to a box with 6 lights labeled for each function.
I am working on trailers 2-3 days a week so it is a necessity for me, not overkill.
Chris