There are apparently two fuel senders. A 2 wire and 4 wire unit. The 2 wire sender is the most common. The 4 wire sender includes the sending unit for the light. Like they said, if your truck never came with the tach gauge cluster or if the sender was ever replaced, the light probably won't work. I would imagine in some cases, the wrong sender might have been installed at the factory as well.

You could probably look at the top of the gas tank and see how many wires are coming out of the sending unit.

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