The transmission brake control switch is designed to keep your car motionless or in motion, depending on the desired operation. The gear shift on your car works in a series circuit with one other switch and an electromagnetic actuator.
One key feature that helps operate the gear shift is the ignition switch. The ignition must be turned on in order for one part of the circuit to close and allow the shifting of gears. This indicates your intention to move the car.
The other key feature in the circuit is the brake switch. The brake pedal must be depressed, with the car started, in order for the switches in the circuit to fully close and allow for you to shift gears. Essentially, car manufacturers want you to be able to keep the car from moving after the transmission is set to a gear.
The switches work in concert with a couple of key safety features. For example, in the event that the gear shift is accidentally moved while the car is being driven, it cannot be shifted to "Park" and suddenly stop the car. In addition, the actuator allows you to shift into "Park" if your car's engine shuts off.
