Well i've totally reconfigured my machine and now have the UP, DOWN and ARC-OK signals coming in to Mach3 OK. In the end I switched to G28.1 height setting which freed up the input used by the probe.

However I cannot get the THC on/off button on Mach3 to do anything ( and yes it is a licensed copy)

If the "Allow THC inputs when not in THC mode" box is ticked, It will work but i cannot stop it, if it is unticked it will not work at all regardless if the THC button is on or off.

Any ideas??