If you want the LED lit all the time the easiest way is to source 12V and Ground from the coin door interface board (below the left flipper button inside the cab) @ connector J2, the pins are marked on the board which one is 12V and which is Ground (Pin 4 grey/yellow is 12V and Pin 5 black is ground) On the button the 2 circled pins are for the LED, + for 12V and - for Ground. For attaching the button to the original button wiring the following is from a message i sent to another FT user some years back BUT the button i used (and the other bloke) only had 3 pins. Yours has 2 sets of the same so i'm not totally positive it will make any difference which set you use as long as they are aligned with each other??
The new switch has 3 terminals in a row (in the middle) and 1 terminal either side (these are the LED 12v and ground terminals). You will see letters beside each of the 3 terminals, these are >> NC (normally closed), NO (normally open) and C (closed or comm). Your original switch should have been wired the same as mine and the 2 wires went to a plug inside the machine. There should be a white wire and a green wire, the white wire goes to NC and the green wire goes to NO. I soldered the diode in the same way it was on the micro switch which is >>> One end to NC and the BANDED end to C (banded end has a grey band around it)