sounds like your doing it right so far. mine was bought with 100% of it's parts , Less the cash box door ! I had to make my own. AND the crap wood from home depot then Fully dried out later & it warped a bit.
original instructions on these type of machines , usually state to clean the contacts, place a piece of paper between them , little pressure applied, and pull the paper out. the paper "wipes" the contact area enough to allow it to do what it has to do. even super light sand paper Can screw the contacts up, scratching off the "silver soldier" that's on them.
my 64 bally is screwed up this way, doesn't work well on pay outs ,ect.
contact cleaner will help, fully follow the instructions, the residue is highly flammable for a long while afterwards. So don't play it for a bit after you use this stuff.... or "FIRE, FIRE,FIRE !!!"
jeff H.