What's not clear to me in the MAD Electrical diagram is why both the red and black wires need to be brought through the bulkhead. In their diagram, the lead from the alternator stud is disconnected from the bulkhead and rerouted to the starter relay. The black wire in the passenger compartment that connected to it is extended almost to the starter relay where it's spliced to the red wire and connected to the relay with a fusible link. The black and red wires formally attached to the ammeter are connected together.

Why not just connect the red wire from the starter relay that already has a fusible link to the black wire inside the passenger compartment that had been connected to the alternator. Then you could eliminate the red wire from the bulkhead to the back of the ammeter and not have to splice the red and black together at all. You could just tape off the black terminal that had been attached to the ammeter or use it for a voltmeter.