Workhorse P3500 Electrical problems by year

This was the first of four incidents, where the starter switch failed. The last time was on march 4, 2014. On the last two occasions, we were driving on the highway at approx. 55 Miles an hour and the engine stopped. No warning, what so ever. All of a sudden, we had no power. We were able to coast to the side of the road. When this happens in a 34 foot motorhome, it's frightening to say the least. In all four incidents, the motorhome ignition switch was replaced, but it keeps happening. The consumer stated the last 2 times,the key turned off by itself and the engine shut off, while driving 55 mph. Updated 04/02/14