Installing ignition relay

You listed a bulkhead bypass? What is this? Just curious.
Also you listed the Ammeter bypass. I'm not sure how you made the connections for that but sometimes just a poor soldering job can cause the issues you describe.
How are you measuring the voltage drop for the ignition circuit?
Engine bay wiring takes a beating from heat, etc. So a worn out wire is still going to be a worn out wire regardless if you install a relay or not.

You came here ands asked for help and this is my $0.02.