electrical issues with the 67 fish

You ought to be able to check the relay on the bench quite easily. It's only a coil which is really an electromagnet which closes a hi amperage switch. Apply 12 volts or so across the coil and listen for the click. Once it does click keep the voltage applied and take an ohmmeter to verify continuity across the switch to see that it closed.

Your problem is probably not in the relay but most likely at the bulkhead connection or the ignition switch. Those relays are really robust and you cannot hurt them with an undervoltage situation.