I realize this is a pretty old post...but I thought I'd throw my 3 cents in (yeah, three). I am VERY VERY new to the motorhome thing, infact the horns on my 74 Argosy MH do not work either. Looking at them from the ground it APPEARS that they are electric... (two wires out of each).
As far as air horns work I have a LITTLE more experience...When I was 18 I decided that I was sick of people (local high school kids mostly) walking in front of my car while I had a green light...I couldn't hit them...the PA system I had installed in my 84 Honda Civic didn't seem to get their attention anymore...what better choice than some Air Horns?!?!!! I went to an auto wrecker "pick'n pull" type place and found myself most of a horn setup (both diaframs, one trumpet, some tubing and the pull switch). I eventually found another trumpet at another place and I was ready... I got a 7 Gal air tank with guage and put it in the trunk...I wired a 12V
emergency tire pump to it via a switch mounted in the dash...when I my air got low I simply pump it up a little...it was good times. This is all to say that when I actually got the horns they sounded VERY weak. I took them apart and there was all kinds of junk and kinda rusty and all that. A toothbrush, some WD40, some elbow grease and several hours later they were echoing off the houses accross the valley like noones business. It was by far one of the best modifications I ever did to that car... (if anyone would like to hear more I'd be glad to blabber)
Well that's about all I had...I was just going to suggest a REALLY GOOD cleaning.
Now I need to figure out why MY horns dont work....