sensing line is off 1 volt at least.
how did you check that voltage. or rather what did you use as ground?
you need to use the case of the vr as ground and verify if it is off even more.
It could be a bad ground to the VR, or it could be the sensing line is dropping voltage through the bulkhead connector.

Typically I just run a relay using the sensing line as the key on trigger and a new line from the battery to the vr through the relay.
Or you can find where the bad connector is and clean it up.