TNalfalfa, went thru similar problem with my new N6 a couple years ago. That included a 'hot' solenoid/relay replacement. Wireing looked great, alternator, batteries checked, ground boltand rings at lower right cab cleaned and looked great. Still had the problem. I noticed the wires were 'stiff' for about the first half inch at the ground rings. I cut off about an inch from all ground rings and installed all new rings. Instant fix and no problem since. Dang thing had 'bout drove me nutier than I am already. May or may not be your problem but if you get as desperate as I did it's something else to check or do. Might add those wires and rings showed no indication of rust or corrosion they were just stiff.
Good luck with that electrical problem especially when you've checked everything and it all looks and checks good with the problem still existing.
Dwight E. Lambert, Albany, Oregon