yes the plug going to the dmd should have 12 and 5
not all the dmds use the 5 volt but all use the 12v
the 2 center wires are GND and the out side wires are 12v and 5v
so black multi meter wire to one of the centre and red M meter wire to one of the out side wires will give you 5 or 12v dc

you should have 12v at BR3 and the cap for BR3 (as i have asked you to check before)
this is where the dmd gets it's 12v from