ptc1937chevy,
You didn't mention if these problems cropped up with the R&R of the switch and coil.
You're right about the 'no charge at idle' deal with the generator. I can't see the connection between the battery tender with or without the battery connected unless the system was backfeeding through the generator when connected.
You would be able to see this on the ammeter I think, in fact while the charger was on and running, the ammeter should show any drain through the system as a discharge.
If you have a voltage tester or VOM, make sure the coil terminal and the fuel gauge terminal are actually dead when the key if OFF.
A battery can short a cell and discharge itself, especially if it is old and heavily sulphated.
Poke around and let us know what you find.
Stuart
