Robert,
Have you checked to see if you are getting air to the horn? Loosen the yellow air line that is in the front overhead cabnet then push the horn button. Doing this will tell you if you have a mud dobber or possibally a stuck reed valve in the horns themselves. If both horns arn't working you could still have something in the reed box.
If you don't have air to the base of the horns open the dash and look at your fuse pannel for the horn fuse. While you have the dash up check the ground buss it will be located on the far left side.
If the fuse is good then you will have to hunt down the air relay valve. It is hid in under the dash. Depending on which model, year, day of the week will depend on where it is located. Once you have found it check to see if you have voltage to it when the horn button is depressed. Unplug the wires going to it and check to see if you have resistance on the wires that go to the coil This will tell you if the coil is good. Also follow the ground wire to the buss and double check to see if the ground is good.
This is just a few things that are simple to look for and hopefully fix. If you can't find a simple fix then go over to
Foretravel Owner's Forum -- ForeForums there are several people over there that have 225/240s and are real gurus on them.