If you don't want to go back and mess with tracing wires or rewiring the panel, you can reprogram the MAME defaults on the "Inputs (general)" menu.
1. Highlight the button/function you want to remap
2. Press enter
3. Press escape to clear that input
4. Press enter again
5. Press the button you want to associate with the function
NOTE: If you reprogram all your inputs using the "Input (this Game)" menu, you will have to repeat the whole process for every single game.
The "Input (this Game)" menu is good for individual games that you want to assign different buttons. i.e. Xybots has a joystick that you twist to turn right/left -- set P1B1 as left turn, P1B2 as fire, P1B3 as right turn, etc to play it using a regular joystick.
Scott