I don't have the details of your machine, but I can give you an idea what happens in most cases of this type of hook-up.
If your control does indeed have a M54 set for this purpose, and it does wait for a finished signal from the indexer, then if you issue a M54 in say MDI, it should hang there and not complete, in the absence of documentation, using this you can find out what phyisical output comes on, either on the output module or card, or in the diagnostic page, (I/O) depending on the system.
The catch now is to find out what input they use for the finish sig.
The easiest way is if you have the I/O listing and schematics for the machine,
once the I/O is found, the signals of the indexer have to conform to the type of I/O you have, i.e. relay or solid state, transistor sink/source etc.
If you have an output card that has LED's on it, the appropriate one will light when the M54 is output.
Hope this helps.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.