No he needs the 7p cable that goes from the power supply to the sound board on the 4 board set.
The 2 board set didn't require that cable just the 4 board set.
RyDawg you can make one up.
There are connectors and pins that will work available at Mikes Arcade,Jameco or Mouser.
They might not make a 7 position connector but you can get an 8 or 10 position and cut it down to fit.
You just need a manual with a wiring diagram for a TKG 3.
I have one that I can scan and email you if you can't find an original cable.