You should test the plug with a wire and a Volt Ohm meeter. As not to damage the plug. Find the schematic and DYODD. .

I, to speed things up, plugged just the board in and jumped the leeds off the positive side, indicated with a +, of the C1 compasator to the voltage regulator 78dl05 (printed on the regulator its self)

Using electrical tape to hold the C1 end to the board whyle also insulating it from other leeds. Also held the C1 jumper end with my finger during testing. Touched the other end of the jumper to the voltage regulators positive leg (indicated by, + IN).

Useing a long enough jumper to go completely around the board to the front side and touch the large exposed leg.

Its easier and you wont accidently run 12v throught something intended for 5v. If a green LED lights your good to go. By default actually testing the wireing harness tells you their is a fault in the board. And you could test the board under power with a VOM. I just did some research. ( Wish their were more contributions here on iFix)