Suspect Firewall connection block.

D67Cuda said
The coil positive terminal only read 4.6 volts

I'm surprised you saw a voltage drop after the ballast resister. Disconnect the coil and test again.

The ballast will show a voltage drop with a load.

Also other places will show a voltage drop with a load.

2.5v is a lot

I would suspect the connector on the ignition switch.

The terminal block on the firewall is reproduced, as are the separate connectors and the individual terminals.

Pull the ignition switch and inspect the connector.