Coil voltage goes from the battery to the key switch through about 14 connections, including the connections for fuses.

Some voltage issues have been resolved by replacing the pigtail connector on the rear half of the switch.

A couple of weeks ago, another issue which was eerily similar to yours was resolved by repairing corrosion damage to connector B-67. B-67 is on the passenger side inner fender between the headlight and battery - I "think" it's under the air filter housing. It's a square connector with about 6 wires. Take a good look at that connector.

Frank