Swapped out a good original to a supposedly New "longer" replacement AC sending unit. Now the unit reads backwards, The light on the gauge is on when full and goes out when low. Swapped the old one back in and it does the same. WTF? Granted that the tank wasnt empty and I plugged in the unit after I installed the unit in the tank. I cleaned both mating surfaces of the plug and unit with electrical spray, still having the same readings. Where do I go next?