Hi,
  is it possible to set one of the inputs to act as the run or start switch when that pin is taken either high or low for say .5 second?
the reason being that I would like to use mach as an indexing head controller.
   Regards
   Tony

Not entirely clear what you are wanting to do but if I am understanding you should be able to set up an OEM trigger to do what you want.
Hood

When you say an indexing head controller - do you mean using your lathe spindle to hold the work, then indexing it round, or are you taking about, say, a rotary table indexing.

The question is really - what method are you going to use to control your indexing head to make it accurate.

My lathe spindle and miller spindle both have an indexer attached which, at the moment, acts as a counter so that Mach 3 can keep track of the speed it is turning, it follows that this signal (which I think goes in on pin 15) also clocks at precisely the same point each time. It is fairly simple to achieve.