MG Car Repair: fuel gauge stays at half full, coolant temp, gauge needle

Question
Hi-
When I start my MGB [1976], the gas gauge needle registers half.  It never moves to show gas consumed or up to full when I put in gas. Any advice?

Answer
Hi Terance,

First test is to turn on the ignition key and have someone watch the fuel gauge. You go back to the right side of the fuel tank and remove the wire (green w/black tracer) (not the black wire) from the flat spade connector. The fuel gauge needle should deflect all the way in one direction. Then touch that Green w/black tracer wire to a ground and note that the gauge needle should deflect all the way in the opposite direction.

If it does that, you have a bad sending unit. (probably rusted into one position)

If you get no response when you removed the wire nor shorted it out, then you have a gauge or wiring problem. If your coolant temp gauge is operating ok, your power supply is ok because it powers both gauges at 10v.

If the needle deflects in both directions as the test above indicates, you can usually just jack up the right side of the car (providing the tank is not full) and remove the sending unit and with the use of WD-40 and careful force on the arm of the sending unit, you can sometimes get it free and working again. This is a common failure and I have been able to save about 50% of the rusted ones this way. (BE SURE TO HAVE THE IGNITION OFF AND NO FLAMES NEAR BY AS THE OPEN GAS TANK CAN EASILY BE IGNITED AND YOU WON'T HAVE A CAR ANY MORE NOR ANYTHING NEAR BY INCLUDING YOURSELF)

Howard