The following troubleshooting guide is from Teleflex Gauges:
The Teleflex fuel gauge and the level sender are designed to operate on 240 ohms (empty) and 33 ohms (full). Most other manufacturers build a marine fuel level system of the same resistance as gauges and senders may be mixed at the boat builder level.
There are only three components to the system-gauge, level sender, and the connecting sender wire. The sender wire should be inspected for breaks in the copper or corroded connection to the terminals.
The fuel gauge can be inspected in the following manner. Turn the ignition on. Remove the sender wire from back of gauge. Pointer must go below the empty mark. Next, connect the gauge sender terminal to ground. The pointer must go above the full mark. If the pointer moves past both E and F, the gauge is functional.
To check the fuel level sender remove wires from sender terminal. Connect volt/ohmmeter to two sender terminals (digital ohmmeter will tend to be jumpy). Ohmmeter should read approximately:
240 ohms @ empty
100 ohms @ 1/2 and
33 ohms @ full.
When the gauge was inoperative on a '94 270 I assumed it was the sending unit, I was happily surprised to find that the gauge had failed, much easier to replace then the sending unit.
