do i need to run a relay with the viair pressure switch? or just wire it like this? i have 12g coming from the battery with a 40a fuse.
no if its the big grey box pressure switch it has a relay built in…
uyou should wireit like the last page in this link…http://static.hornblasters.org/diagrams/mnl-hbtw-icas.pdf the "ignition wire mean a “switched power” wire that gets no power when you turn the car off…
ONLY use the gray box style with a single compressor onboard air system, or you WILL kill the pressure switch, and/or relay from too much current being passed through the included relay. Max relay amperage for these is limited to the relay, which is a 30/40 amp relay inside the gray box.
Cant get a better answer then from Lance himself.