The KeyWiz is designed for 2 players.
8 of the inputs are labeled Up/Down/Left/Right for Player 1 and Player 2. 8 of the inputs are labeled 1-8 (8 buttons for Player 1). Then there are 16 inputs labeled A through P (8 buttons for Player 2, plus 3 coin buttons, two start buttons, Enter, Tab and Esc). There are also two ground terminals, a +5 Volt terminal and an input for the shift (Shazaam) key.
Apparently you can program your own keys, but I just stuck to the defaults.
Oh yeah, it comes with a chart that tells you all the key defaults for each terminal on the board.