that two pin connector is used to turn on the door bezel (yellow back lit piece). it puts out a +5 vdc signal, so polarity is in play. compare your other plug on the other machine to where the wires connect to and copy that connection. the two pin connector was used to connect a WBA unit, going back to the 200 unit you will have to either find the older style plug or modify yours.
I have the older style plug (I save them when I convert the machines to a WBA).
as far as the dollar conversion, you will have to replace the coin in head, use a cc-16 instead of a cc-33 and harness , move the four plastic cc holders from the inside position to the outside position, change out the black encoder in the coin in optics, move the coin chute on the door panel, change the shelf wheel and add a star agitator to your hopper. and change the dollar decal on the reel glass, you will have to have a set chip to set the denomination to 25 cents. I have all these parts.
Hope this helps
Jim