This Fan-Thom II kit comes with a threaded thermostatic switch that screws into the extra coolant temperature sensor port of the passenger engine head on Generation III and up GM engines for a professional looking installation. This inexpensive protection for an electric fan and a vehicle's wire harness. Provides constant voltage, protects from voltage and amperage spikes and prevents the fan from back feeding voltage through the vehicle's wire harness. This kit includes: Weatherproof SPST 40 Amp relay, weatherproof 30-amp circuit breaker, M12x1. 5mm thread thermostatic switch 205 degrees on/190 degrees off, weatherproof relay base with harness, weatherproof heat-shrinkable crimp-on terminals and mounting hardware.