our Jayco 17.55 AT van has the tow secure breakaway system, also has sway control. all brake control goes via the tow secure breakaway unit which is powered from the house battery.

After a 9000km trip it needed some wheel bearings and new hubs (spun bearing) also 2 of the brake magnets were dead.

All together again and the brakes hardly work at all either the breakaway pin or when driving. albeit the handbrake does work well. I've checked the wiring and all seems ok except voltage drop...

I disconnected the connectors to the all 4 brakes, with all circuits open 13.5V at each with the breakaway switch activated, with one brake wire connected voltage drops to 12.5V, with 2 brake wires connected voltage drops to 11.5V, with 3 brake wires connected voltage drops to 10.5, with all 4 brake wires connected voltage drops to 9.5V? 

Does anybody know if this is normal? doesn't seem right to me? If it is what could be causing the brakes to not work?