None of the actual charging amps goes through the ignition switch. The ignition switch does send positive voltage to the alt or regulator, Depending on the Alt setup. Stock, the + went to the Regulator from the Ign switch.

Do you have the 4 wire Denso as shown in the above diagram? If so it does need a light or small resister to energize the alt. But, you say your light has never worked. I say move up to a one wire as suggested.

Your big Positive output wire to a bulk head, non factory on the fire wall is fine. But, it does make it tougher to get your motor to lose + volts with the trunk mounted kill switch. Is that operational now, as wired previously? If not, time to address that as well.

But, Whats wrong with your ignition switch. You can turn it back a notch and lose charge voltage. Most switches are {Acc/Off/Run/Start}. So you have {Acc/no,charge/Run/Start}. That doesn't make any sense to me, maybe just a Wore out ign switch that you can rotate back in between {Run/Off}, killing power to the alt or reg. But I think Denso,s have there own built in reg.