Gas Gauge Not Registering

[pdawg]

I need some advice on an ongoing issue I'm having with my gas gauge. I have replaced my send unit - twice - and completely gone through a troubleshooting guide that I got off this forum, but still have a gauge that only ever registers a maximum of a quarter tank. Since I had a bad replacement I metered the send unit before I installed it & all was good. I have removed the send wire - gauge registers full. Grounded the wire at the tank - gauge goes empty. Metered the wire from tank to fuse box & from fuse box to gauge - all good, have 12V on other terminal of gauge. pulled out the instrument panel & checked the printed circuit board - cleaned all contacts, replaced burnt out bulbs. I don't know what I'm missing, but it has to be something as it still is not working. Help please !!