Just put new 3/8"" sending unit in my 70 Challenger 440RT. Have it out of the tank and checking it out--can only get 1/2 tank reading on gage when float is fully extended. When I ground out the blue wire, I get full gage deflection. I have a good ground on the sending unit. Any suggestions? I hate to rip into the dash (cuz I just put it all back together ) Any suggestions on what my options would be will be appreciated