Thanks for correcting my false assumption.
Still, something is not right. I plugged in a servo cable again, plane is armed, motor is running, and rpm1 is 0
Dang, this is worrisome, RELAY_PIN and PIN2 self reset to 54 and 55. I put them back to -1.
Ok, now I'm seeing 6000 again, unplugged the servo, stilll getting 6000 with nothing plugged in (is that normal?)
then I plugged my RPM wire from the ESC, and still get 6000.
I power cycle pixhawk, have it reboot, still get 6000 (with ESC RPM wire plugged in)
I unplugged the ESC RPM wire, power cycle pixhawk, stilll get 6000
Plugged the ESC wire back in (white/signal wire pointing down on the pixhawk, like the other servo wires), used a Y cable, measured voltage on signal wire and saw it go from 0.2V to 2.xV when revving motor.
During all this time, rpm1 is still 6000