Thanks for those details. I have a possible route going under and back I need to check out some more. First I have to do some more measurements like time2roll suggested. Also I will do the jumper cable trick to check out the pos and neg paths individually in case there is a problem with the frame neg path.
I don't expect the isolator to be guilty since it is not an "isolator" with the 0.6 voltage drop, but is a "solenoid" with the small voltage drop--according to the story on that. We'll see.
I am not fussed about having an isolator anyway. My Chev has none. If isolation is desired, you just yank the fuse in Stud 1. With a 7-pin you just unplug that. This Ford has the solenoid and a CB instead of a fuse. Just have to get used to it :)
