Here's a cheap 6 volt reducer... Don't like those resistors that get too hot?   Tired of those expensive voltage drops that end up fryin'?? How about a cell phone charger?  These can be found at most electronics surplus stores. It takes 12 volt DC and reduces it to 6 volt DC at 2 amps. Cut off the cigarette lighter end and hook it to 12 volts. At the other end is a jack, open up the charger and solder on a couple output wires.  Hook up the output side to your gas guage and that's it!    You can find these for around 2 bucks!