where is this power supply you intend on switching or not youve not included one in your specifications and to include an electric pressure washer you will indeed need a place to draw power which in itself would be a switching mechanism you'll need to add a generator (gasoline or lpg) or your endevour will not be self contained and you will be limited as what you can clean by the availability of electricity on site should you fail to rectify this situation in your design this is not criticism only guidance

looking to make a mobile detailing trailer for a small business... i have a 250 gallon water tank that if i add this pump will it supply enough water to run a small electric pressure washer without starving the pressure washer. or damaging the pump itself? (http://www.harborfreight.com/lawn-garden/pumps/12-volt-marine-utility-water-pump-94639.html) would i have to add on a switch to turn on/off power ?