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.  An absolute necessity if adding a dash mounted manual on/off switch to your electric fan circuit. This kit includes: SPST 40-amp relay, 30-amp circuit breaker, relay base with harness (6' input, 4' output), crimp-on terminals and mounting hardware.