Aftermarket fuel gauge

Make sure your gage is for mopars, as far as ohms go. It should be 90 to 10 ohms,or real close to that. GM gages will not work.
Is your tank grounded, either thru the metal fuel line at the tank, or like I did. I put an extra ground wire from my tank to the frame.
Otherwise, start checking all your grounds, at the dash, tank, and in-between.
The gage has to be grounded also. It should be marked on the back, with a separate ground wire. Check the whole length of the blue wire, make sure its not pinched, somewhere. Dave