Is it simple to test the control unit at all?

I have one and put grounded the earth wire and put the other 12v wires together just for testing, plugged in a gauge and the sender unit and nothing.....

Should it or ideally does it need wiring into the main unit?

Cheers

I've read your post twice, but don't really understand what you've done, nor what you want to achieve.

Can you be a bit more specific? IIRC, there are earth, permanent live, switched live, and lighting wires to the control box, the gauges just plug into gauge and c/b using dedicated links provided, and the senders plug into the c/b ditto.

Alcazar