I was just working last week on a VMC760-16 with a 4th axis. It looked like it had a 36 pin connector! This one had a Siemens motor in it. It had the pins for the Heidenhain encoder, pins for the temp fault, triggering of the hall effect transistors, power, enabling jumper, etc.
I had to reload the hard drive so I know that on this machine, I used a 4th axis enable disk I carry from Bridgeport.
On the TC4, there was a kit for a 4th axis. I have installed one. It included an additional drive, wiring and plugs that mounted in the arm going across the top of the machine to the CRT. And parameter changes.
The indexer was an option also. That included the necessary solenoids to allow it to function.
Typically I believe Bridgeport used Troykee 4th axis units. You have to make sure that for the TC4 there is the proper Yaskawa motor in it,