Ok, now the picture gets clearer! Somewhat!!
The door on this machine is one the earliest doors. No bet button, no spin button, no credit meter or cashout button. Only the handle can spin the reels. So all wins would be paid immediately. Now the main board has a daughter board at location 1A. The function of this daughter board is for determining credit limit, etc. Not needed for a machine with no credit meter. But leave it there for now. Slot program may need it.
I asked about the grey/white wires because they are needed with a Yellow Dot power supply. Seen older machines without them, but yours looks to very old and yet has them?
They use the 110v outputs to power door lights (flourescents)
The meter lock not needed at all, jackpot lock can be replaced with three position toggle switch.
Your voltages sent me looks like Yellow Dot power supply. 4A fuse ratings also say Yellow Dot. You have a Tower-4 board in power suppy. This board is for the handle.
Since you are seeing all 8's in the Win meter it sounds like a board problem. But make sure the power supply has a good 5vdc. You stated 4 volts in pm, must be 5vdc. Not sure how good of meter you are using?
When you power up the machine, open the door, a 50 should flash in the Win meter. If nothing, you have board problem or bad 5vdc to board.
I know you tried a ram clear. Are you doing it right?
With door open and machine OFF, remove hopper to get better access to board reset button. Press and hold black reset button in. Now, with other hand, turn machine ON. Hold reset button in for three seconds and release. Machine should make bleap-bleap-bleap sound. Win meter should have a flashing 50. If not, board and/or power supply problem.
Jim