I have everything wired, except the esc key.
I have 6 buttons per player, so they are wired to the position 1-6 on my I =PAC 2.
I have 2 open spots on each side of the I-PAC 2 (positons 7 & 
Where should I wire my esc button?
Do I just do it to 7 or 8 and adjust it using the software?
Or is there a default on the I pac for esc (without shifting)?
What is the default shifting combination for esc?
Thanks!
Lots to cover here:
Manual -
http://www.ultimarc.com/ipac2.html - Start there and the links should cover most everything you need to know.
I like a dedicated Pause and Escape on the panel.
Note that the shifted Escape method mentioned below may give you problems in a 2-player simultaneous game when both player want to continue playing at the same time and the game quits.
A better option if you only want one additional button is to set a button for pause, re-map it to be the shift key, and then have another shifted button for Esc. So for example, pressing Pause and holding it and pressing P1Start (or P2Start, etc.) quits the game. This requires reprogramming the I-PAC, though.
If you just want to add a button for escape, just wire a new button to P1Button 7. This is "C" by default.
Now you have two options -
Option 1 - If you will only be using MAME, just go into TAB - Inputs (all games) - and change the key for UI CANCEL to "C" (or "Esc or C"). This avoid re-programming the I-PAC, but you will have to do this for all the programs that you want to use the I-PAC with (and if some of them don't allow you to re-assign keys, it won't work).
Option 2 - Re-program the I-PAC so P1B7 send "Esc". Now the I-PAC will work with most of the programs out there and you don't have to adjust MAME or your other software.