I have a Haas 5C indexer, similar to eBay item 310175166880, except mine
is a stepper driven model. It has a chuck on its nose also.

The way it works is that you program it like a VCR, and upon pressing
a button, it advances one step of the program. You can, say, specify
that it needs to divide a circle in 23 divisions. There is a provision
of a remote button at the end of a two conductor cable, and it can be
wired to the CNC mill.

Which is what I did.

Now the mill can use the M64 and M65 G codes to tell the indexer to
advance. I wrote a G code subroutine advance_indexer that does its
namesake job using M64, M65 and waiting.

After this I added a GUI button "advance indexer".

I used an "audio extension cable" to provide a disconnect capability.

What is really amazing is how easy it was. I was tired, garage was
cold, I made several dumb mistakes (like forgetting to install a DC
SSR into the slot that I wanted to use), and yet the whole job took 2
hours from start to finish.

Thank you, EMC2. Also kudos to Jon for his easy to use PPMC system.

i