I added a 10a 6v to 12v converter to my 49. To keep it from drawing with the key off, I wired the inverters input off of the spare switched terminal on the ign switch and also wired it's output through one of those inexpensive 12v auto relay's and fused it. This way the input and output is switched and fused.
So far the only devices I'm powering w/12v is a tach and cig lighter/power port. The rest of the truck's electrics is 6v.