Hyundai Repair: Hyundai Accent fuel gauge problem, hyundai accent, accent 4

Question
I am working on a 1999 Hyundai Accent 4 door sedan. The fuel gauge was not reading correctly. With a full tank of gas, the gauge would read only half. Half a tank of gas would read a quarter tank and so on. Today I replaced the fuel sending unit that I ordered from the dealer. I took the tank down and replaced the part and put it all back together the way I took it off. Put the tank back up and drove to the gas station and filled up full. Now the gauge doesnt work AT ALL....  So now I am extremely frustrated and dont know what the problem is. Help...

Answer
To start, go to the fuel pump/fuel sender connector and unplug it.  But this time, don't drop the tank.  Pull out the rear seat bottom and there will be an access panel below the seat.  Remove that and unplug the connector.  Turn the key to the on position.  The gauge should read empty.  Then short together pins 3 (black wire, ground) and 4 (black/white wire, level signal).  The gauge should go to full.  If the gauge reacts as it should, then the problem resides in the tank.  If not, then you'll need to check the wiring and fuel gauge itself.

If the problem is in the tank, here are some things to consider:

I don't recall how the sender attaches to the fuel pump assembly, so I'm not sure whether it's possible to wire it incorrectly.  If so, that could be the case.  If the parts diagram is correct, there are three wires with eyelets you need to screw on.  The fuel sender incorporates a thermistor and float.  You'll need to make sure that each wire is attached to the appropriate place.  You'll need a continuity tester to see which lug goes to which terminal to which wire in the harness.  Here's the key:
Pin 1 -- Blue/black wire, thermistor input for low fuel lamp
Pin 2 -- Yellow wire, Fuel pump power
Pin 3 -- Black wire, ground
Pin 4 -- Black/white wire, float signal for gauge

Similarly, I've seen units that can be installed in a different orientation than the original.  This can prevent the float from raising and cause the gauge to always be on empty.

It's possible you didn't get the correct part.  According to the catalog, you should have received part number 94460-22021.  

It's possible there's an open circuit in the fuel pump mounting plate.  You should find this when you test to see which lug goes to which pin in the connector.