2004 F350 Super Duty. The engine is a 6.0L diesel (I think ... it is my friend's truck; I know it is a diesel of some sort).

The power windows circuit breaker is fine, but there is no voltage to the terminal in the under-dash fuse block that it plugs into. Using a wire to jump power over from a nearby 30 amp fuse terminal makes the power windows work as they should, so the problem has to be somewhere between the battery and the power window's circuit breaker terminal.

I doubt it is a broken or otherwise damaged wire, which makes me suspect some other component (e.g., relay, module, whatever) that power must go through before getting to the power window circuit breaker. Any ideas where to look?