univolt III wiring

[McGill]

I removed the airstream univolt III when I replumbed my 68 tradewind.
No I've put all the wires back, but I don't have any 12 volt action.
I have 110 volts AC the univolt III hums.
But doesn't put out any 12 volt juice.
Question? There is a white ground wire coming from the breaker box in the back near the univolt.
It is about long enough to reach the univolt III, but I can't see anywhere that it would hook up to the univolt III
Whee does this wire go? and would that
keep the univolt from working?