My brothers truck has unusual problem of when parked the horn randomly comes on and stays on?
Any ideas as to why?

 

I had this same problem on an 2012 Jeep wrangler and it was diagnosed as a bad "clock spring". Other than that I can't help - good luck and keep us posted as to the final determination of your problem is.

Dan

 

If it was the clock spring, would the air bag light be on? Would it just come on after sitting parked all day? My first thoughts where same but people said air bag light would on?

 

On the Jeep - and that's my only experience - no warning lights would come on at all. First time the horn started sounding I was driving it - horn came on - sounded for several minutes - I had pulled over and tried to figure out what was wrong - the horn stopped sounding on its own. Then had several incidents of the horn sounding on it's own while the Jeep was parked. No warning lights were ever present. Jeep Service said it was a bad clock spring and replaced it.

Yes it would come on while parked all by itself - middle of the night a couple of times - day time once or twice.

 

Thanks mate, that's good info!