The trigger switch assembly is the housing where the AEG circuit breaks. There is a trigger trolley that bridge copper panels to close the circuit. These trigger switch assemblies are standard to most AEGs. However more modern iterations have chosen to install mechanical click switches or programmable electronics to replace it.
At its core it is simply a switch designed to operate the circuit that turns the AEG’s motor on or off.
The housing is shaped to allow the trigger trolley to slide through while a spring captured by the trolley is hooked on the gearbox shell that keeps it from making any uncontrolled movements. High voltages and current can burn the contacts which is why the installation of a MOSFET is recommended to prolong its lifespan.