I ran more tests this AM and the Raymarine ACU controller is putting out a little over 6v (plus and minus) in each direction with motor disconnected. I did notice the meter numbers were dancing indicating the voltage was not constant. My raw tests with 12v were not comparable, and that's when the motor worked. Will call Raymarine again about this, as their published test is vague about voltage.

Checking the Rudder Reference Unit Raymarine linear rudder reference p/n M81188, I measured within the parameters below. Still stumped.

The test numbers I published last night are for the rotary reference. According to the Raymarine support forum, the Rudder Reference Test for M81188:

Red to Green: 5K Ohms (+/- 10%) Steady
Red to Blue: Variable no less than 1.5K no more than 3.5K as the wheel is spun hardover to hardover.
Blue to Green: Variable no less than 1.5K no more than 3.5K as the wheel is spun hardover to hardover.

The Red to Blue and Blue to Green may not go all the way to 1.5K or up to 3.5K, but whatever either is at midships, the deflection should be about equal to either direction(i.e. midships 2.5K if is goes up to 3.1K, it should go down to around 1.8)