Clutch Start Safety Switch
The clutch start switch is a member of the starting system. It's a safety device that prevents a driver from starting the engine with the clutch engaged. It's usually mounted on the clutch pedal assembly but may slide on the master pushrod.
If the switch is stuck open, the vehicle will not start. If the switch is stuck closed, the vehicle will start even with the clutch pedal out and the clutch engaged. This is dangerous. Use a multimeter to diagnose the clutch switch and circuit. Remove the switch's plug and test it for battery voltage with the meter's voltmeter. Set the meter to measure ohms and check the switch for continuity. On a good switch, the meter should display infinity with the switch open and the pedal out, not depressed. When the pedal is depressed and the clutch is fully disengaged, the switch is closed, and the meter should display continuity or close to 0.00.
Most of these switches are adjustable. This procedure is usually performed while adjusting the clutch pedal travel. The switch contacts a stop on the pedal. Check for any TSBs and special procedures or specifications in the manufacturer's repair manual when adjusting clutch pedal free-play.