Re: Pressure washed the truck, now horn sounds like crap!
give it a few days. it'll dry out. and next time be careful where you aim that pressure washer. infact, i think it's a good idea to stay out from under the hood with it period. use it to wash the frame, suspension and maybe inside the wheel wells.
water under that sort of pressure can find it's way into electrical connections and torment the hell out of you down the road a few months/years.