My low gas light is on. I have replaced the gas pump and have full tank in the

No I was very careful when I installed the pump. Why isn't the back sending unit working? Is there anything that could be wrong? I checked all the fuses I could see in the cab. Edit I just checked the old sending unit and it works just fine. So I still have the same problem.

Let me get this straight, you have the old sending unit , you plug it into the vehicle harness , and the gauge works? , then you plug it back to the new one and the gauge doesn't work? OR how did you test the old sender?

With the unit on the floor I cut the wires to the sending unit and checked with an ohm meter. the lowest reading was 40 ohm the highest(full tank) was 260 ohms. So to me that says the old unit is working. When I checked the plug, before I did any thing else with the plug off the pump, The top two were hot the bottom two were grounded.

I'm still confused (but don't worry , that's easy for me) , but , before you changed the pump , was the gauge working properly?

No that's why I changed the pump. The light came on when I thought I had a 1/4 tank But not sure about that. I filled the tank no change. The light was still on. Every thing I read and every one said That the sending unit was bad. So I filled the back tank,light still on. Both sending units bad at the same time. I don't think so. But changed the pump any way. When I checked the wires in the plug The two top ones, purple and gray were hot. The two bottom ones,orange and black are grounded. Is there a relay some where? I don't think both wires should be grounded. Found the problem. A chaffed wire at a slice under the cab. Thanks for your help. AL