I used to work in industrial automation. The Fanuc robots used Harting connectors. The dark grey metal housing/connector is basically a tough quick-connect for electrical cables.

For the Fanuc robots, they would provide power and position information for the servo motors. Sometimes one housing would serve more than one servo motor.

I haven’t seen anything like in OP’s picture but I can see how the modular internal connections could be a wiring nightmare.

Industrial machinery for interconnecting modules for example.