My Hella airhorn compressor has a positive and negative terminal. I'm using the relay which has a connection grounding it to the car. Which terminal on the compressor am I supposed to hook the wire running from the relay to, the positive or negative?

 

Relay wire to + terminal on compressor but you must also run a wire from - terminal to a ground.

 

Aha! Thanks for the help!!! So you need a ground from the relay and you need one from the compressor too. They don't tell you that in the instructions. Gracias amigo!

 

Yes the relay has 4 terminals, 2 for the "coil" and 2 for the "contacts" (switch). One contact terminal goes to a 12 volt source (fuse box), the other contact terminal goes to the + terminal of the compressor. One of the coid terminals goes to ground, the other to the "trigger" that is to make the horns blow. The easiest "trigger" to use is the hot lead from the existing horn. This actually puts 2 relays in the circuit (the cars existing horn relay and your new one) and creates a slight time delay but it's not a big deal.

BTW the coil leads carry little current and can be small wire, the contact wires need to be larger gauge.

 

Got them working. Boy are they loud. Loud like the airhorns you hear at football games, just not quite as bright.

 

Which model did you get?

 

Just make sure you connect it to the right one?