I have a 1991 240 DL. The horn works sometimes and sometimes not. Basically, while I was driving and pressed the horn, most of time it did not response, especially when I needed it most to alert other driver. But sometimes when I assumed that it was non functional and pressed on the pad, it responsed. I would say about 80/20 that it would not response when tested. I have not run direct current from battery to check the horns since it did work when it wanted to. All the fuses in the panel were cleaned recently and in good condition. Please advice!!

 

Check the ground wire(s) on the horns. Being at the nose of the car, the horns are exposed to the elements allowing the ground wiring to corrode where it mounts to the chassis. Loosen it wire brush and replace. Also check the connections on the horns themselves. Less common but equally simple, the horn contact in the center of the steering wheel can corrode.