Low voltage problem

1966 Plymouth Valiant
Older style VR

Suddenly noticed voltage is 12.4 when car is running, verified with multimeter.

All connections looked good.

Based on another thread I first measured voltage at alternator with engine off, same voltage as battery.

Next, I connected a jumper from the field connection at the alternator to the battery positive, started the car and monitored voltage, revved up the engine, no increase in voltage.

I removed the alternator planning a rebuild thinking I had isolated the alternator as the problem.

Roundback alternator with one field wire.

However, I didn’t disconnect the field wire from the alternator before performing the jumper test.

Did failing to disconnect the field wire invalidate the result?