depending on how did you modify the stock underdash harness to feed the voltmeter and bypass the cluster ammeter system, will rule what would you need to rewire that into the aftermarket ammeter. And that's something what only you know.

the deal is you can splice any wire coming from alt splice down the dash harness to the ammeter, but the wire to the batt MUST BE just one, the one coming out from + lead of ammeter to batt/starter relay stud. You can't get other one but that one between ammeter and batt.

In other words you can even run a straight wire between alt post and ammeter keeping the existant wires from the alt side in place BUT YOU CAN'T run the same between ammeter and batt. All the batt side of the wiring MUST GO THROUGHT the ammeter