Another Fuel Gauge Problem

[Mr. Green Jeans]

Hey Guys - I have a 72 custom Camper. This week I was pitting in ten bucks worth of gas and my son and wachted the fuel gauge go all the way to full and is stayed there. Since it's all original I figure the gas gauge went bad. I just put the new one in and now it reads wayyyyy past the full position...almost up side down. I know I put the gauge in right because of the dummy lights. Wiring looks fine (but not tested) where should I go from here??? Thanks