A glow plug relay test is an engine troubleshooting method that involves using a multimeter or test light to check the power reception capability of a 7.3L IDI diesel engine. The test determines which engine connection is faulty and whether the connection between the ignition and the relay is sound.
Conduct a glow plug relay test if the glow plugs in the engine have been replaced, but the glow plug system is still not functioning. It is important to first check if the glow plug controller has good ground before moving on to test the relay. The engine should supply 12 to 14 volts to the positive lead at all times when the ignition switch is engaged; if the proper voltage is not being supplied, it is necessary to replace the relay.