[dvldoc]

You would have to tap the wire, to check it with it connected.

But if your getting 4.5 volts with it disconnected that means that is the 5v input wire. The output wire cannot put out voltage if the connector is not hooked up.

80% of the time it's the middle wire that is the 5v output. Just use that niffty little blue tap we put in the kits, Screw it down on the wire and touch the voltmeter to it.