I want to rig up the dual air horn/compressor setup so that the steering wheel activates the horns when the engine is running (or accessory in on position) and activate the stock horns when the engine is off.

Reasoning behind it being that the compressors drain 40amps each.

#1. If the car is left with the alarm on I'm worried about draining the battery if it's triggered over and over

#2. Compressors have lag, and the pulsating that the alarm puts out barely makes any noise. It just spools up the compressors.

So that's the situation

 

Just measured stock horn if anyone is interested. 2.8A@12.5v each.

 

The Power Lead on the battery!

Chris

 

My battery stays charged with the engine off

 

Mine does, because I have a small solar panel sitting on top of my dash. It actually works really well!

Chris

 

Here is what I did. I was no longer using the power plug relay, and that gave me a switched wire. I extended this wire out of the fuse box and have used it to pick the relays I've added around the truck. Not sure if this will work for you, but I try not to splice into wires used by other devices.

 

Another revelation: the current coming off the stock horn wire is not enough to drive an air horn!

Just ran a 40amp relay straight from the battery and to the compressor. There is no delay now and it's 'twice' as loud! If the alarm is triggered it is actually beeping and not only making the compressor spin up.