I recently purchased a new fuel tank and sending from MACS. I installed them last week and have driven the truck several times with no problems. Today I went to hook up the electrical and when I turned the key on, the gauge shot all the way past the full line. I only put around 5 gallons of gas in originally. Any ideas on what the problem might be? I did not use the original wiring harness because I plan to replace it but I did substitute a new wire and hooked it up just as the old one was. Yellow wire on my Truck. I plan to call MACs tomorrow but thought I would throw my dilemma out there for any ideas. I sure hope it's just a rookie mistake. Thanks

Edit - Just wanted to add that my electric system is 6 Volt Negative ground. They also did not include instructions so do I have the wires backwards? Live wire to the center screw and ground to the prong???

 

I would try it with the ground to the outside and gauge to the center. It all works off resistance to ground, which is why it's probably reading full. The resistance is equal as both are directly connected through the frame/metal of the vehicle.

Either that or the ground at the instrument cluster could be bad or not connected.

 

If the yellow wire goes to the back of the gauge, that goes to the center terminal, even if you are really 6v (-) ground. Are you really negative ground?

 

I think that I just installed the same sender. If so, it is supposed to work with original gauges. From what I understand, the original sender and gauges ran on 1.5 volts. This reduced voltage is sent to the sender from the gauge. Maybe you have something other than the original gauges?