I had used 12v pumps before the are very finicky break snap overheat and plastic guns, lets face it will do the same. I am going to be adding soft washing to my services, and i'm using my smaller MITM 3506 and Two tanks, Two ball valves,and a agricultural spray gun that is adjustable at the gun from wide fan spray to jet stream, right at the gun tip, oh and its made of sturdy steel, less likely to break. Here is how you save yourself from burnt out 12v pumps!
Here is the gun:
<a href="http://www.amazon.com/Gun-Spraymax-Pest-Control-Inlet/dp/B000KFCQPW">GET YOUR GUNN!</a>
Switch from high pressure to low with the switch of a gun. Without spending the extra money, to me the only difference is, no running back and forth to the truck or screaming to your guy to shut it off, and blowing 129.99 everytime the pump fails! I guess the only thing you'll save is gas but what about batteries on your vehicle, those get expensive right? Call me crazy I guess!!