Fuel Heater

Using an ohmmeter, check resistance between terminals. There should be more than .7 ohm at room temperature.
Remove vacuum switch from fuel filter and check continuity between terminals. No continuity should exist. With vacuum of 7.8-11.8 in.Hg. (200-300 mmHg.), check that there is continuity between terminals. If switch fails either test, replace switch.
To test fuel relay (located in left kick panel), Test for continuity between terminals 1 and 3. Check terminals 2 and 4 for no continuity. If continuity is not as specified, replace relay. See Fig 1. To inspect relay operation, connect battery voltage between terminals 1 and 3. Check for continuity between 2 and 4. If operation is not as specified, replace relay.

Fig 1: Checking Fuel Heater Relay