The switch cuts the tool on/off and is a very common part to replace. There are many different types of switches and many will look, operate and install differently on nearly every tool. There are many varieties of switches that offer forward/reverse, variable speed and locking features; there are single pole/single throw, double pole/double throw switches and many in between. You can use a multimeter to test the switch for defect, but some have circuit boards and make this difficult. Make sure wires are secure, soldered and not burnt. If the tool is intermittent or won’t turn on/off, also check the brushes and power cord.
This item fits the following models:
15-pc Thunderbolt Black Oxide Drill Bit Set
1/4" x 50 Ft Noodle Air Hose with Coupler and Plug