Servo amp connections needed. Where should I go from here?

I have a servo controller that I can't seem to find any information
on.

It is manufactured by Control Systems Research, Inc. Pittsburgh, PA.

The model is NC121F.

My question is in trying to get control of a servo motor with a
single or stacked potentiometer.
The controller has signal and tac inputs. I do not know what it is
expecting at these inputs. My first guess was 0 to +10v at both
terminals in relation to the common. I don't really have 0 to -10v so
I am unaware if a null point could be reached this way.
My mode of thought here is that the tac may output 6-7vdc/1000 rpm.
If the inputs were tied together then they would track each other.
Not so, or at least it did not prove out.
When I touch either the tac input or the signal input with one wire
or my fingers. The shaft slows and stutters . Possibly the stray ac
signal I presume from my overhead lights. Using another power source,
it was found to reverse the motor direction by connecting the signal
lead to ground.
Am I way off base in my mode of thought for bench testing this
setup?

DC