Review on Mega Blast Air Horns: Ultra-Loud Black Air Horns for Trucks, Cars, SUVs - Train Sound Guaranteed by Jason Wesley

I put in two separate switches, one to turn the compressors on and off at all times and the other to use the horn. I haven't had to use it in traffic yet, but I enjoyed scaring a few innocent passers-by. I uploaded a video showing the difference between a regular horn and a mega blast as I drive down the street. You can load one later from outside the truck.