I believe you're Dart is build like my 72 Demon. If so , remove the drivers kick panel and locate the connection that goes to the rear of the car and unplug it . Locate the wire that goes back to the fuel sender. Use a jumper wire and short the side that goes to the gauge momentarily (5-6 seconds) with the ignition switch in run position . The fuel gauge should rise toward full. Do not leave it connected long. If gauge rises it is probably ok.
Using an ohm meter connect it to the wire going to the sender. There is a page on this FABO site that will give you the reading approximate to the fuel level in the tank. If no reading check the sender ground. There should be a strap by the senders that spans the short hose connecting the sender to the fuel line. Make sure it is making a good connection. A lot of these problems are ground related.
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