Morgans wrote:

At cruise RPM? Sounds like you may have 1 or 2 of the three diodes
burnt
out in your alternator. Another possibility is that your voltmeter
is off.
Try checking it with a digital voltmeter, and comparing the two.

Any RPM between 800 and 2700 gives the same voltage, no change. I
normally read the voltage in 4 ways
1) My EDM shows it on the screen
2) My regulator flashes a voltage light on my panel when low
3) My voice annunicator says, "Check bus voltage" and
4) My A&P has been putting his probe all over the place

Since I can reproduce this at idle on the ground its easy for the A&P
to hook up under the panel. I should also note that...
1) Have a new battery, new master switch, and new regulator
2) I took my regulator and alternator to an aviation electrical
overhaul shop. They bench tested the combo at 14v up to 100amp draw.
They didn't find any diode issues, but I'm willing to believe they
could be wrong.

-Robert, M20F '76