Welcome to our Complete Kits catalog. We design our Insanely Loud Kits with everything you need from start to finish to have train horns installed on your car, truck, SUV, or just about anything that has a 12V power source! Tank and Compressor units that are separated are fully sealed units that are able to withstand the elements when being mounted outside. Now any Tank and Compressor unit that are mounted together aren't fully sealed units. Those units will have to be mounted somewhere out of the weather/elements. Kits with the same name but different model numbers consist of the same horn but different tank and compressor combinations. The bigger the tank the longer the blast time with the Horn. And the bigger the compressor can either mean a faster refill or a stronger duty cycle to allow for other pnuematic uses such as using air tools and airing up tires.