diy thc

Is that a board made by you?
Are you trying to wire that board ?
Picture of the bob ?
The thc up, thc down and arc ok go to bob inputs, the +V and -V should come from the plasma cutter divider, not directly from torch and clamp.
Parallel port inputs are 10,11,12,13,15.
You also need a floating switch if you want it to be fully automated and sensing the material.
No need for limit switches or you can wire them all in series and use the 1 input that is left.