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MG MGA - Guage reads Empty or Full

The fuel gauge in my 58 A reads empty when the ignition is off normal)and full when switched on. There is no in between reading. When the car is running, the needle is buried on "F".

Is this indicative of a faulty gauge or more likely the sending unit or another elctrical gremlin? I know Barney has some test protocols for fuel gauge faults. I plan to do some testing, but I was wondering if anyone has experienced this same situation.

F Valenzano

Gauge pegged on full could mean open circuit in the sender unit or disconnected sender wire. Check the snap connector in the engine bay near the starter switch for the Green/Black wire.

Check sender unit resistance. It should be 0 ohms empty, 70 ohms full, and roughly linear in between. Use an ohm meter. Disconnect the wire from the sender unit and check resistance from bottom terminal post to ground on the tank (sender shell), and to ground on the chassis. The fuel tank MUST be grounded to the chassis for the sender to work. Original tank ground was through the steel fuel pipe to the fuel pump. If the pipe is cut and connected with rubber hose you could lose ground for the tank. In that case add a grounding wire from the tank to frame.

If resistance through sender unit to chassis looks okay, then reconnect the wire there. Disconnect the sender wire from "T" terminal on back of gauge, and check resistance from the wire to ground on the chassis (dash should be grounded). This should be same resistance as seen at the sender unit. 50 mega ohms is open circuit (disconnected).

If sender wire behind dash has the correct resistance for proper signal, then the fault may be a broken wire inside the gauge (but check the sender circuit before fiddling with the gauge).

Reference articles here:
Barney Gaylord

This thread was discussed on 09/04/2010

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