MG Car Repair: Fuel Gauge vs Sending unit, gauge system, fuel gauge

Question
I have a 1979 MGB.  Today the fuel gauge stop working, all the other gauges work fine.  I removed the fuel gauge there are 4 wire in 2 bundles of 2.  One , black + red/another color they go to the light bulb. The second bundle is 2 wires green with another color.  How can I check the gauge and the sending unit.  Thanks

Answer
Hi Luis,
I the dealership we worked out a quick rough test to check the gauge system. Go to the sending unit and you will see two connectors, one ground and the other to a insulated flat spade connector. Turn the key on and unplug the insulated wire and the gauge should deflect all the way off scale and then ground that wire and the gauge should go all the way off scale the other direction. If it does that, the gauge and the wiring is probably ok and the sending unit is at fault.
If it does not do that, you either have a bad voltage stabilizer, bad gauge or a wiring or fuse problem on the green wires.
Howard