I have been wondering for some time how to add dedicated add-coin switches to my cab, so my guests wouldn't be bothered remembering the I-PAC shift key for inserting coins, etc. I really hate the idea of adding extra buttons for MAME functions onto my control panel, so I wanted them to be logical and inconspicuous. Then it dawned on me that there are 2 buttons on almost every cabinet that go unused as inputs -- the coin reject butons! Hmmm....

A quick fumble thru the spare-parts bin turned up 2 small microswitches with roller levers. I cut off two small chunks of wood to be used as spacers (about 1.5" x 3/4" x 1/4") and screwed the switches securely in place on the wood. Then I placed double-sided tape on the backs of the wood, and pressed them into place on the upper coin chutes, so that the switch actuators would be in contact with the plastic wedges that get pushed down by the red reject buttons.
Then I wired across the common terminals of both switches, and ran this wire to the coin door's "test" switch, with another wire running from the switch down to the ground wire on the original coin mech switch. This allows me to "cut" the ground that runs to the reject button microswitches, so that tokens must be used to play games if I desire. Otherwise, I can get credits by either pressing the reject switches, or inserting tokens in the coin slots.
The two reject microswitches have wires connected from the NC terminal, to the NO terminal on the corresponding coin mech switches. This means that the reject switches are held open by the plastic wedges, and become closed when the wedge moves downward as the coin reject buttons are pressed, and the microswitch actuator arms are released. The reject buttons only need to be pressed in about 1/8" before the switch is closed, so a large amount of credits can be quickly racked up!
Obviously, I am using the reject buttons as the 5 and 6 buttons in MAME, but you could wire them to act as any two buttons. They could be secret shift or shazam! buttons for example...
