We had a similar problem in our 172M. The over voltage detector was
firing at too low a voltage, and we would get multiple dropouts.

To simplify diagnosics we used a handheld electric motor and Vee belt
to drive the alternator and then an adjustable power supply or fat
resistor load while looking at the 14 V lead with an oscilloscope. It
is a lot better than working around a spinning propeller. Found the
problem right away.

I noticed that the original overvoltage wiring "blob" had a small
tweekpot adjustment screw showing on one end. I suppose we could have
adjusted the trip voltage a little higher with that, but we already
had purchased a new one. Pipers may not be the same.

BTW - when measuring voltage drops, be sure to measure across as many
faying (joint)surfaces as possible. Your resistances sounded kinda
high.