Hi PWD,
You don't mention what you referenced #6 to: conventionally you would have the black Voltmeter probe to pin #2, and the red probe to pin #6. If that is where you had the probes, the variation of the reading would make me think that either you do not have a good connection with the probes, or that you have an internal connection that is not well made, like a cold solder joint.
Here is how I would have made the measurement when I was an active troubleshooter:
I would connect all the connectors you show in your photo, so that the motor, battery, and all ancillaries were properly connected. make sure the drive wheel is not on the ground.
Then I would measure the voltage between the red (red probe) and black (black probe) wires on the back side of the throttle connector. You should have a constant reading of about +5 VDC. If that is not the reading, I would suspect a bad connection in the wiring harness or control board . It may be difficult to make the probes connect with the contacts inside the black connector. Small diameter probes would make it easier to make contact.
Then I would measure between the blue (red probe) and black (black probe) wires. With the throttle closed, you should measure low millivolts. Alan can probably give you an exact range of readings. As you roll on the throttle the voltage should increase smoothly, and when you hold a constant throttle opening, the voltage should remain very steady. If that is not the result you get, the throttle would be suspect.
TTFN,
Dennis