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 is 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: SPST 40-amp relay, 30-amp circuit breaker, 12x1. 5M thread thermostatic switch 205 degrees on/190 degrees off, relay base with harness, crimp-on terminals and mounting hardware.