Air horn issue

City horn working properly,but air horn don't. Checked the fuse and already changed the solenoid! I'm horrible with all the wiring work but I'll give it a try.Any help is much appreciated! The truck is 99 Volvo with S60 engine.

 

I took apart the steering wheel and trying to find out if the air horn button works. There are two wires responsible for the both horn. When I touch the black one to the ground(metal part of the steering column) the city horn is activated . My question is how to activate the air horn from those wires? Of I do that than obviously the problem is in steering wheel button . Thanks in advance!