Fuel Gauge & Low Fuel Warning Relay
Disconnect wire at fuel tank unit except on 1966-69 Imperials. On 1966-69 Imperials disconnect wire from terminal marked "Ind" on low fuel warning relay (located on lower right instrument panel near glove box). Connect one lead of suitable tester (C-3826) to wire terminal and other lead to a good ground. Turn ignition on. Turn tester knob to "H" position and observe instrument panel gauge. Gauge should read FULL, plus 3/32" or minus 1/32". Turn tester knob to "M", gauge should read 1/2. Turn knob to "L" and gauge should read EMPTY, plus 1/32" or minus On all models except 1966-69 Imperials the low fuel warning relay will trigger the low fuel or Sentry Signal Lamp when the gauge pointer is moving from the 1/2 position to EMPTY.
On 1966-69 Imperials if gauge does not perform as prescribed, inspect for an open circuit paying special attention to printed circuit board. If circuit continuity has been established, replace gauge. If gauge functions properly test low fuel warning relay as follows: Disconnect wires to terminals marked "Ind" and Tank" on relay and connect one lead of ohmmeter to terminal "Ind" and other lead to terminal "Tank". The ohmmeter should read 7.4 ohms plus or minus.3. Remove lead to "Tank" terminal and connect to a good ground. Ohmmeter should now read 750 ohms plus or minus 35 ohms. If relay does not meet specifications, inspect for a poor ground at attaching screw or corroded or loose connections at terminals and repeat test. If relay still does not meet specifications it should be replaced. If both panel gauge and relay tests show them to be operating properly, proceed to test for fuel tank sending unit.
On all other models if panel gauge does not perform as prescribed, continuity of circuit from tank sending unit to panel unit should be tested with special attention to printed circuit board before replacing gauge. If panel performs properly when tested but fails to operate properly when connected to vehicle system, fuel tank sending unit ground strap should be inspected for proper installation on fuel line. If ground continuity is good, remove tank unit for testing.