Hi Pip, and welcome to the forum.

First things first, and before the greater and better drag their arses out of bed - you mention a Boxford 160 - I expect this is a lathe?, and it's been converted to Mach3?

That conversion is going to have introduced a whole bunch of unknowns in terms of how the conversion has been implemented. From the outset I'm going to say that I have no knowledge of that machine or the controls around the tool changer, and even someone that knows the machine won't know how the conversion has been done, so I'd recommend getting some decent photos together around the toolchanger (so we have some notion of what sensors/switches there are) and particularly around the control electronics, break-out board (BOB) and so on. The more information you can offer the more chance that someone will be able to offer some insight or help.