@ Rob - I like the cut of your jib with the flamethrowers idea!
@ Sparky - Very easy to do this but you need a 5 pin 12v relay rather than a 4 pin unit that is rated accordingly for the circuit you want it to switch (Though most are either 20A or 40A and are capable of switching most general electrical items). As above by Ian_S, don't try to run something with a heavy pull as you will come out to a flat battery and get "click, click, click, click" from the starter.