If your good with electrics (I'm not- but getting better), and don't mind spending some money then you could consider the sPod or Switch Pros systems.
I like the Switch Pros because its a solid state system with auto Mosfets so you don't have to worry about fuses/relays and it is relatively straightforward to setup.
However, if your feeling adventurous go for what has been suggested in the previous posts the choice is yours