MG Car Repair: Fuel sending unit, gauge wire, fuel gauge

Question
Just bought a 74 MGB.  The fuel gauge doesn't work properly.  Reads full until it gets to about a 1/4 of tank then drops down.  When I looked at the fuel sending unit it only had one wire connected to it.  Looked like a new unit.  As I crawled under the car and looked at the fuel pump I noticed it looked like they took the ground wire for the sending unit and used it on the fuel pump. I assume this cause that wire and the wire attached to the sending unit come directly out of the same harness.  What is the correct wiring configuration.

Answer
Frank, both need a ground so add a ground wire to the sending unit before any thing else. If it still does not read correctly jack up the right side of the car high enough to not loose gasoline and remove the sending unit and plug the hole with a rag or such so as to avoid the gas fumes gaining access to any spark you may cause. Connect the gauge wire and a good ground and turn on the key and manually operate the sending unit arm and watch the gauge to see if you get the correct response. Some times the unit will get rusty and stick, thus causing unusual readings.

Howard