Bulkhead Instrument panel bypass.

The second plan is to convert to the ‘80s-‘90s style wiring. Simply connect the alternator output stud, via some serious gauge wire (matched to your alternator’s output specs) to the battery stud on the starter relay. But be absolutely sure you splice in an appropriate length of fusible-link wire into this new conductor! Here’s what gauges to shoot for:

Alternator output rating Wire gauge Fusible Link
Under 50 Ampere 12 16
50-65 A. 10 14
85 A. 8 12
100 - 120 A. 6 10
With this done, the bulk of the charging system current will no longer flow through the firewall connector - or the ammeter. Obviously, the ammeter will no longer be accurate. The plan here is a simple accessory voltmeter, which should have its positive (+) side wired (with practically any gauge wire) to any ignition-switched 12-volt point, and the negative (-) side to ground.