Hi John
Thanks for your reply.
That sounds like a good plan. So if I`m reading it right, Pin 16 gets the signal from Mach3 - tells the relay to release the 5v. When pin 16 drops the signal the 5v returns to zero ?

Please bear in mind I`m a complete dunce with electronics, I`ll need to be shown how to build the relay circuit.
any help would be very appreciated.

I want a dedicated PC for this project and have cobbled together an oldish system
AMD Athlon XP 1800+
1.53 GHz
640 RAM

On the Xylotex there is 5v available on the small connector where I have stuck the Limit Switches Common wires. It`s marked VCC is there anyway I could tap into that ? ?

EDIT :: 3 mins later
I have just turned on the system and physically touched the TTL signal wire for the valve onto the VCC 5v on the xylotex
and yep the valve looks like it`s working.