Just bought a 2004 292 Fastech and need to know where the air horn compressor is located.

This is where it is on my 353. Not sure if its the same but worth a shot.

I know the horn is located up in the port gunnel. Previous owner installed another on the starboard deck with compressor underneath the helm. I think the factory compressor isn’t far from the horn location

The compressor is inaccessible on the port side basically. Do yourself a favour, get your self a new horn and compressor from Amazon. It will be louder than the original. I went through this already on my 2004 292.
Very reasonable price too.

This threads a couple of months old. The horn compressor is relatively easy to access. First you need to remove the wire that attaches to the engine compartment fire extinguisher. The other end of that wire is the manual discharge t-handle. The t-handle is attached to the access panel that has to be removed. Once the panel is removed. You you can remove the hose, +/- wires and unbolt the compressor from the bracket. I take it apart annually. Clean the veins and the can. You'd be surprised of all the debris that's inside. Hope this helps.

do you mean in the engine compartment?