The ipac comes programmed to the mame defaults. I.e. player one directions are the arrow keys, P1 button one is left control, etc. if you changed these in mame you need to change them back, (press tab in mame and select "change settings for all games" if you have never programmed the Ipac with WinIpac.
For your three non shifted admin buttons, you need to wire them to 1A, 1B, 2A or 2B on the ipac. for example, to map your pause button to "P" which is the mame pause keystroke, you'll need to use WinIpac to program that button, say its connected to 1A, to register a keypress on 1A as "P". This is all well covered on Andy's site and that's a better resource than my rusty memories. I set and forgot all this stuff over a year ago. Also, admin is "tab" and and exit is "esc" for mame.