When I fill up my 69 the gauge goes to full, but when it gets to empty I still have a half tank. Its a nos sender and original gauge. Any advice?

Inside the trunk, you'll find plug with a tan wire. This goes to the sending unit.

Unplug and on the body connector, the harness going to the dash, ground the tan wire and see if the gauge will read EMPTY. If not gauge needs work.

Measure the tan wire going to the tank sending unit with an ohmmeter or DMM in Ohms function. Full tank is 90 ohms, half is 45-50 ohms, and empty is 0 ohms, but not an exact science.

If tank is empty and gauge shows half tank, the float rod may need to be bent, a "field calibration" done to make the gauge work. This is providing the sending unit does go from 0 to 90 ohms and the gauge indicates what the sending unit is sending to it.

Weird,..it almost has to be a bad sending unit, but do as instructed above just to double check your guage. You can ground wire at the connector which is also used for your license plate light. The guage should drop to empty.

If I ground it and it goes to empty would it mean anything. I mean it goes to empty now, the only problem is I still have a half of a tank when it does.

It sounds like you need to adjust the float so the gauge reads "empty" when the tank is almost empty. I like to have a little gas left when the gauge reads empty just to be safe.

Could you make the guage read 'empty' by grounding the sending wire or sending wire connector?...(as Everitt explained above).

If so, your guage is fine, your sending unit is bad. If not, I'd blame the guage.

Good luck

He has already stated that the gauge will go from "full" to "empty", but when on "E" he still has a half tank. The float needs to be adjusted.

Perhaps,..and perhaps the old float isn't floating. But short of dropping the fuel tank, I'd conduct a five minute test to ensure the fuel guage is reading what it should,..full (or past full) with open loop,..empty with a grounded wire (the tank to guage wire). 35+ Year old fuel gauges do go bad.