1991 Dodge Ram electrical problem ?

I know this is going to sound crazy but it is really happening and I need help ASAP. My cousin has a 1991 Dodge Ram 150 pickup w/318 engine. The pickup can be sitting still running and will cut off, turning the key with spin the starter but it will not crank. (Here's the crazy part) blow the horn one time and the truck will start. If you are driving down the road when it knocks off all you have to do is blow the horn and the engine will catch and start running again. You can unplug the horns and if it knocks off it will not start again until at least one horn is plugged back in. I know this sounds crazy but it is true. He has replaced the fuel pump and computer. If anyone can help it would be greatly appreciated. Thanks.

wrong wiring at the steering wheel? That's all i can think of...

sounds like a fualty ignition switch...