New: alternator, voltage regulator, alternator belt, and battery cables. Battery checked out good too. Voltage is around 13.8 with hot engine running and nothing else turned on.

Problem; when I put a heavy electrical load on i.e. headlights and a/c the voltage ramps down over several seconds and the warning lamps light up on the dash. Like the alternator just goes off line for some reason and I'm running on battery only. Eventually the voltage sinks low enough for the engine to stumble and quit and I'm left with a weakened battery that may not start the engine again. If I run just the lights or a/c alone, this doesn't happen.

Voltage drop tests between battery and alternator all seem good. I was thinking that maybe the excitation voltage to the alternator gets cut off somehow and the alternator stops working. But I don't think it needs excitation once it starts putting out amps.

I don't know what to do!
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