ViAir 12 volt 40 amp relay.
 
For use with all 12 volt compressors. Relays work with compressors that fill air tanks by utilizing a pressure switch. Te relay acts as a buffer between the compressor & the pressure switch, which can burn out prematurely from experiencing full amp draw of a compressor. 
 
A tab molded into the relay case, provides a secure mounting point to protect electrical connections.
4 prong relays allow a 12 volt item, to be switched on & off when provided with power. Always use a relay with any 12 volt powered item, that is hard wired into your vehicles electrical system.
Rated to a maximum amperage or 40 amps.