I've got power to the hot side of the ammeter - it is the only spot inside the dash that has power. I assume the FL is OK since there is power on that red wire all the way from the battery, through the fuse block and to the ammeter.

I found a wire diagram for the dash wiring and am trying to figure it out. There appears to be a junction of some sort where multiple wires cross - the one feeding the horn in the fuse block; the one going to the headlight switch; and the one for the battery feed to the fuse block. Not sure what the junction is. I've attached the edited wire diagram showing the wires and junction of concern (at least I am trying to attach it...)

I think I may pull the whole harness this weekend and test each line. If that does not do it, time to get some cash and go with a new set of wires.