This SOUNDS like corrosion between a battery post and a connector, or at the other end of the high amp cable.......the sypmtoms are pretty classic for a "normal" car, in that a large draw of power kills the connection, but often a weak draw will cause it to "come back on". I wonder if you have some corrosion say between a post and a connector on the 12 V battery. It's not always visable....they have to be disconnected and brushed to know.

I realize the dealer has it now......I would be curious about what they find.

Hmm, that's interesting to know. If they can't figure it out this time, I'll suggest that they look for the corrosion.

Thanks!

The classic symptom is that when someone turns the key to start, everything dies.....all power. It comes back when they let off the switch, or sometimes the car sits for a few moments, or when a battery cable is jiggled. The next time it may start, or may repeat.

It's different here of course in that the 12 V system isn't trying to spin a starter, but I'm sure it's flipping a few solenoids. I'm not sure what else exactly.

Ususally there's gnarly corrosion in these cases, but I've seen it a few times where someone sprayed a thin film battery protector BEFORE they attached the cables to the posts....it all looked nice, but there was actually a thin layer of some kind of crud. And if someone has replaced a battery clamp, where it attaches to the heavy gauge wire is subject to the same issue.

The general symptom is a heavy draw kills the connection. Light draws may work OK (radio, interior lights, instruments, etc.)

After spending the weekend at the dealership, Ford replaced the master cylinder.

I quote from their work sheet:
"Cause: 21647 050805A 1.6 VCC Found multiple codes including C1524, perform diag and TSB 050805, RR MASTERCYLINDER and service bleed retest all OK"

They claim that both the brake malfunctions and the power loss are both caused by the master cylinder problem. While I made it back to work OK, I will let time tell if the power loss issue is fixed or if I need to investigate the corrosion possibility.