if you don't want to add a ghetto looking switch, use the rear window defroster button that is stock, just disconnect the defroster and splice into the stock wires for power. it should have enough amperage rating because they take a lot of current. if you don't disconnect the defrost, your neons will go off after your back window heats up and shuts off

 

i always thought it'd be cool to have it hooked up to a generator on a belt attatched to the engine so the higher your RPMs are the brighter the neon glow is