This photo was taken for something else but it does show the location of one of the Grounds in a Mad Catz TE
This is under the button distropution board and not the main PCB.
See that wire I soldered there. The Left side of that wire is the main Ground or GND as its labeled on the PCBs.
The other last 2 ends on the right is the KGND and it is for the tournament lock (as it disables start and select).
You only need to mess with KGND on special circumstances or to bypass the tournament lock. So forget the KGND, some TEs will not have the KGND.
You can locate the ground side of the board by noticing the traces, the bottom side of this pic, you see all there terminals connected by the same trace.
There also spots to solder to on the Main PCB and the guide PCB, but the button distro PCB is you best bet.
I chosen this board because is easy to access to, easy to solder too and no components to accidentally burn