[markcee]

As a follow up to this, after finally getting the umbilical wiring correct, I was still left with no trailer brakes. I ended up isolating the issue by following some advice received on a Ford forum, as it seemed the simplest next step. I cut the brake wires at each wheel and reconnected them one wheel at a time, plugging in the truck and trailer and testing after each reconnection. I had braking on every wheel until #4 was reconnected. Still have to solve that issue (consensus from the Ford guys seem to be the magnet), but thought I'd pass on this straightforward method of isolating the problem. It was easy for someone like me (dummy with a multimeter) to accomplish. Even if I end up taking the trailer in for the final fix, at least I will have braking on one axle (I was advised to disconnect the working brake on the problem axle to avoid any pulling to one side).