Showcase Cab Control Panel Question

[Japedo]

If this has been gone over before I apologize, I searched and did not find anything.

I recently purchased Tekken 3 in a showcase cab.  I'm about to purchase a Street Fighter PCB and need to wire in the extra two buttons.  I think the cab might be prewired for the extra buttons.  I think it might be prewired because the control panel already has precut holes where the buttons would go, and there is a harness for players 3 and 4.  Also in test mode on the button function test, the buttons are "shadowed."  I was hoping someone has a wiring diagram for this cab, I believe they are built as generic cabs then they just throw in the PCB.... I could be wrong though,  I don't know much about these, but before I purchase and install the kick harness, it looks like the cab is already prewired for it. 

Thanks for the help in advance.