Gas gauge reads empty to 1/4 only

[72ArizonaBurb]

I pulled my instrument cluster and ran jumper wires from the connectors to the back of the fuel gauge. I also installed a separate gound wire. Gas gauge would still only read 1/4 tank. I then connected a spare gas gauge I have and it went to 3/4 of a tank. I tested another gas gauge I have it when to 3/4 of a tank. Looks like I had a bad gauge or the small circuit on the back of the gauge was bad. I am glad to have this figured out. I will add a separate ground when I re-install it permanently as suggested by several memebers.