Ammeter pegged to plus on my 74 318 duster?

First, is it possible something is taking the battery down? Glove light/ radio on? Take a voltmeter and see if it's regulating or over charging (voltage) Depending on if the battery is low or high, "normal" running voltage should be 13.5-14.5. Much higher than that shows it's overcharging


Second thing to do is unhook the regulator to see if there is some problem in the under-hood harness or in the alternator. If that does not stop it charging, unhook the field (push on) connectors at the alternator ONE and then the OTHER, and see if one/ other/ either stops it charging.

If unhooking the regulator stops it, check the ground on the regulator, might be loose/ rusty.

If it's grounded, and pulling the regulator plug stops charging, probably just a failed regulator.