Chris

I had the same problem as you once, only I gave up. Our semi tractors (Peterbilts & FL) use the 11 o'clock & 1 o'clock for tail & clearance...they split the load so you don't necessarily lose everything if one fuse/circuit goes out. Then I bought a air-operated elec brake controller. I think it's a Kelsey-Hayes product. That may solve the brake problem...not sure.

I think also that using the powered relay type mechanism as Boog etal show above is probably going to be the answer.....I guess.

We use 7 pin on everything...semi type 7 pin, not RV 7 pin, trucks, pickups, little trailers, big trailers, wagons, etc.