Terminal 2 is feed to lights, not ground. Presumably terminal 1 is +12, so terminal 2 (if connected to a load) would have variable volts, depending on dimmer position. If no load connected you would of course measure +12 volts, regardless of dimmer position.
Correct for 3.
BTW OEM radio, pw switches and atx lever position indicator all work off of dimmer so presumably you don't have those or you would have noted them being blacked out.
