The reference plate and tool setter are the same item (I think). Which 5v wire are you referring to? To use a touch plate you can use a piece of pc board, measure it's thickness, solder a wire to it, connect that wire to any input pin available, assign that pin in Mach. Check the diagnostics page when touching the plate to the metal of the machine, the led representing the pin it is connected to should light up. You shouldn't need to worry about ground as the machine is grounded.