I decided to move forward with the voltmeter. I will wire it as follows:
Wiring changes for a voltmeter, and use even thicker wire (AWG 6/8) in the engine compartment. Of course, my current crimpers can't handle these terminals, so I had to buy a new crimper too (Wiha 32841). An excuse to buy a new tool isn't entirely a bad thing.
I also realized my old Vette has an Ammeter, though that car has a generator and probably puts out 25A +/-. Either way I'm going to check the circuit and connections carefully.