Fuel Gauge And Tank Sending Unit Checks

The fuel sending unit for the Bugeye and Spridgets through the 1964 model year are the same. 

If you gauge reads backwards you probably have a early/late mix of sender and  gauge. The change over took place in the 1965 model year. I think the MGA is the same as the early cars and the MGB is the same as the later Spridgets.

Check the fuse. Probably not the fuse since a Bugeye only has two and other things would have stopped working also.

Check the "hot" side lead (Green) by running a test wire from the fuse block. Wire may have broke somewhere along the way. Stuff happens.

Measure from ground (base of unit) to the wire spade connector.

Early Tank Senders (Based on measurments taken from a new gauge by Hal Cummings)

0 Ohms Probably a broken lead wire. Maybe a bad ground.
14 Ohms = Full
90 Ohms = Approximately 1/2 tank.
258 Ohms = You ought to be lookin' for gas.

Later Senders (Based on Numbers Found on the Internet)

0 Ohms Probably a broken lead wire. Maybe a bad ground.
30 Ohms = Empty
120 Ohms = Full

This is not a linear scale so I'm not sure what 1/2 would be on the later senders.

If you have removed the sending unit:

Check the movement of the float arm. This should move freely. Try some WD40 if it does not.

Make sure the internal contacts are not corroded. Clean these up the best you can then use some electrical contact cleaner on them. If the corrosion is really bad you may have to replace the unit.

Make sure the wire connection points to the front of the car when unit is installed. The float must be toward the center of the tank to work correctly.