not a mopar

IIRC, the alternator/charging light get turned off by a wire either from the regulator or the alternator that when the alternator starts charging it applies power to the ground side of the warning light & that's how it turns the light off. I don't know what color wire it is specifically & what type of system is in the Pinto to know if it's wired to the regulator or the alternator since I don't have a schematic for it. But that is basically the way it works. It could just be the connection at the regulator or a broken wire to the light. I'd tend to believe at this point the alternator is ok since you have 14.2V coming out of it & the regulator is at least doing it part with regards to charging. If I can dig up a wiring diagram or a schematic I'll PM you & send it to you.