Hello all, happy holidays. Wanted to say thank you for all the great posts in this forum. I have a 95 ford ps that was having issues starting after sitting for a while (cold starting). I determined the problem to be a bad glow plug relay after reading several posts in this forum. During that time I sent an e-mail to a friend of mine who is a mechanic at Ford. He sent me some troubleshooting tips off of there system and I thought I would post them here. The information says 95 ford pickup (7.3L Diesel) but I'm sure this can be used for most powerstrokes.

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Glow Plug Testing

WARNING: DO NOT by-pass the timed pulse function of the glow plug system. A constant 12-volt current to glow plugs will cause them to overheat and fail within seconds, possibly resulting in severe engine damage.

Check Glow Plugs
With ignition off, disconnect glow plug connectors at glow plugs. Connect a 12-volt test light between a convenient power source and each glow plug terminal. If test light illuminates, go to next test. If test light does not illuminate, replace glow plug and go to next test.

Check Harness
With ignition off, disconnect glow plug connectors at glow plugs. Squeeze sides of glow plug module protective cover and remove cover. Using an ohmmeter or test light, check continuity between each glow plug lead and test terminal of glow plug module. If all leads check okay, go to next test. If any lead has an open circuit or is shorted to ground, repair or replace lead as necessary, then go to next test.

Check Control Unit
Ensure ignition switch is off. Measure resistance between glow plug module ground wire terminal eylet and negative battery terminal of each battery. If less than one ohm is indicated, go to next test. If greater than one ohm is indicated, clean or repair ground connection, then go to next test.

Check Voltage From Ignition Switch
Connect voltmeter positive lead to glow plug module ignition terminal. Connect volt-meter negative lead to ground. Turn ignition switch to ON position. If voltage is 8 volts or more, go to next test. If voltage is less than 8 volts, check fusible link, repair wiring or rechard battery as necessary. Go to next test.

Functional Test
1) With ignition off, connect a 12-volt test light between glow plug module test terminal and ground. Position test light so that it can be seen from driver’s seat. Turn ignition switch to ON position and monitor test light. Compare test light times to chart. Total test light ON time includes time from the beginning of the initial ON cycle to the end of the last ON-OFF cycle measured in seconds.

NOTE: The WAIT-TO-START indicator and/or test light may not illuminate if engine temperature is at or near operating temperature.

*Control Unit “Wait-to-Start” Indicator Test Light
Temp “ON” Time (Sec). Total Time (SEC)
-20 degrees C 7-15 35-70
0 degrees F 7-12 25-60
35 degrees F 5-12 15-35
70 degrees F 3-5 7-15
105 degrees F 1-3 3-5
140 degrees F 1 or less 1-3

*Temperature of control unit, not ambient temperature.