Is the 2.5 connected to a cutting machine?
If so what type?
The OEM usually has a relay for plama start to the Max 100.
I dont remember the terminal numbers on the Max 100. I am on the road and do not have a manual handy.
I think Start is 33&34 and Arc On is 36&37. Check your manual first.
If your cutting machine has Oxy fuel already connected to the 2.5 then you will have to wire up a special Relay interface, as the 2.5 does not have enough I/O for both.
Let me know what you have.