[Bakin76]

I have a 71 Challenger with a non-rally instrument cluster. The fuel gauge always showed empty. The previous owner told be that the sending unit was good and the gauge needed to be replaced. I replaced the gauge and now it always reads full. Please help - Thanks!

[dave-r]

Always reading empty is usually a sign that one of two things have gone wrong.
Most common is that the earth strap that connects the sender outlet tube to the fuel pipe is missing or corroded. The sender grounds through the fuel pipe so there should be a clip-on strap that jumps the short rubber section joining the pipe to the sender.

The second problem could be a faulty 5 volt supply to the gauge. There is a voltage reducer on the back of the dash that supplies the power for the sender.

However a gauge that reads full and is pegged to the far right is a sign that the 5 volt supply is working but now you have a short circuit somewhere in the wire to the sender or in the sender itself.

I may be wrong but my guess is that there has been a short circuit there all along. The previous owner fitted a new sender which made no difference. Then the gauge burnt out as it would eventually. Now you have fitted a new gauge and it is being effected by the short again.

Your new gauge will fail too if you do not fix this.

If you use the search facility you will find previous threads about faulty fuel gauges and the various tests you can do to test each part of the system. Including measuring the sender to see if it has the correct resistance to read the fuel level correctly.

Good luck.

[Goldenblack440]

great diagnosis there! And nice lateral thinking about the reason. Makes sense to me.