The amp gauge works the same on 6v or 12v, it is just showing current direction. Unless the temp gauge/sending unit was replaced with an electric one, it does not take power except for the light. It is a continuous unit from the bulb to the gauge. If damaged it won't work. The speedometer does use electric power except the light. The gas gauge issue is better addressed by doing a search. There are several common problems and trouble shooting guides that can be found fairly easily.
Chuck
