Hi guys,
The TCS system does require some extra hardware over the basic ABS system. It uses the wheel speed sensors of the ABS to detect wheelspin, but has an additional pump and valves fitted to the hydraulic actuator. The pump and valves are used to braking apply pressure to the spinning wheel, diverting the torque to the wheel with most traction. It also closes the throttle plate to reduce the engine's torque output and match it to available traction. The braking of a spinning wheel only happens at lower speeds (up to 30MPH I think), over this only throttle plate adjustment is used.
The switch isn't necessary for the system, it is only used to override it should you want to. The system is switched on by default. If you have the system, the TCS warning light in the dash (next to the airbag light) should illuminate for a few secs when you switch the ignition on. It also flashes when the system is in operation.
Here is a pic of the TCS switch in my Mondeo, it is next to the heated seat switches below the stereo:
Paul.
