1970 C10 Battery/Alternator/External regulator issue

[broberson]

I’ve got a ‘70 C10, battery keeps going dead when I’m running lights. Here’s what I’ve gotten so far..

1. Alternator is 2 wire external regulator, running, the battery leads show 12.8 volts, lights on it drops to 12.5V..

2.Battery is new, holding at 13V charged and unhooked.

I need to know, where does the original wiring w the external regulator, the brown wire goes where? The ignition switch? I’ve had overheating issues with the wiring, which is why I don’t currently have it plugged in at #4 on the regulator.

What’s the problem? Alternator or regulator?