nobody writes:

I've never actually seen a TCAS unit, so I'm not familiar with the turning-on
procedure.

There are many different types of unit, anyway. Additionally, TCAS may be
integrated into other instruments, such as navigational displays, in which
case it isn't turned on separately. There's no standard for such functions as
avionics go, so variations are considerable.

There is a standard for the way the traffic is displayed, however.