I started learning about Land Rover fuel gauges when I decided to add a tach to my instrument panel. The large gauge hole that holds the temperature and fuel gauge was the perfect donor for a tach. When I went to replace the fuel gauge with a 3 inch round Smiths gauge, I quickly discovered nothing worked. Suddenly it was time to learn about Land Rover fuel gauges and sender units.

The gauge

Fuel gauges are thermal gauges. The more current that is run through them, the hotter the metal strip that moves the pointer becomes and the farther the needle travels. Thermal gauges do not care what the polarity of the current is. Negative or positive earth is the same to a fuel gauge.

What matters is the amount of current traveling through the metal strip. A quick way to identify thermal gauges is that they take a few seconds to read properly after you turn the ignition on. Some gauges are designed to have the needle point all the way to the right when there is minimum current flowing, and some gauges are designed to have the needle point to the right when there is maximum current flowing. If you don't match the gauge to the sender unit, it will read wrong AND read the opposite direction as the sender is trying to indicate.

The sender unit

A sender unit is a variable resistor whose resistance varies by the height of the float. Electricity flows from the battery, through the gauge, to the sender unit into ground and back to the battery.

Remembering that the gauge reads the amount of current flowing through it. The sender units limits the amount of current going through it by how high the float level is. The variable resister on the sender unit can be built to pass maximum OR minimum current when the float is in the empty position. It is important for gauges and sender units to be matched.

Land Rover fuel Gauges

The series cars have two types of gauges with matched senders. One is for the positive earth Land Rovers and one is for the negative earth late IIA and series III Land Rovers. They read in opposite directions from each other. Therefore you must be careful to match the sending unit with the gauge.

The early style sender unit has a small metal tower on the top. The later style sender unit has a flat top with everything mounted below the top. They are physically interchangeable on the petrol tank but must be matched to the correct gauge. The after-market Lucas fuel tank sender unit replaces the series III sending unit and will not work with the early gauge.

Moving away from factory stock

When I installed a tach in my instrument panel's large double gauge hole, I added a 3 inch fuel gauge on an auxiliary panel. Later, when I installed multiple fuel tanks, I added matching fuel gauges to monitor my fuel supply.

There are a number of Smiths 3 inch fuel gauges available from various British cars that would look "factory" on a Series I - IIB Rover's instrument panel. I used gauges from a MGB.

All of the non-Land Rover Smiths fuel gauges I have tried work with the series III sender unit and a voltage stabilizer. The earlier positive earth sender will not work with any other Smith gauge that I tried.

Since Land Rovers factory wired for positive earth do not have voltage stabilizers, I added one to my car to provide the correct voltage to my Smith's MGB fuel gauge.

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