What kind of voltage reducer - "Runtz" type?

http://www.classicparts.com/1947-54-Gas-Gauge-Voltage-Reducer/productinfo/24-995/#.WPimDxLyudE

That type reducer is directional - the reducer at the link can only be installed in one direction (no mistakes). Wait to hear from someone else regarding which post it attaches-to - if you attach to wrong post, you fry the fuel gauge.

Good luck.