Glow plug relay

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Aug 24, 2010 | 02:06 PM

mabc926

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Glow plug relay

I went down today to put on my new starter relay and when I was getting ready to try and start it again I noticed that my glow plug light wouldn't come on when I turned my key half way, I was guessing this meant my glow plugs were not on so I didn't even try to start it.

So why isn't my glow plug light coming on?

I was thinking it might be the glow plug relay.

Aug 24, 2010 | 02:08 PM

mabc926

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And on a side note when I turned the key to half I didn't hear any clicking from the glow plugs.

Aug 25, 2010 | 01:05 AM

Festus Hagen

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From: Maine (NorCal Native)

***** The following assumes you have already checked cables, connections, cab, chassis and engine grounds. *****
***** When testing energize briefly, long enough to get the answer, no need to overheat things and no more than 10 seconds *****

Unplug the forward most (towards front of truck) connector on the Injection pump, this prevents overheating the FSS.

*** Glow Plug Test. ***
Test light test of the glow plugs:

Unplug the Glow Plugs.
Attach one end of a test light to 12v+ battery.
Touch the other end to the terminal on the end of the Glow Plug (where you unplugged the harness)
Does it light up?
- Yes, Chances are it's good.
- No, Replace with Motorcraft/Beru ZD1A for 83-86, ZD9 for 87-94.5.
This test is susceptible to miss diagnoses and should only be used for a quick reference.
To do a positive test use a volt/ohm meter and test the ohms between the terminal and base. Should be .5 to 1 ohm resistance.

Test that you get power to the glow plugs:

Unplug a glow plug.
Attach one end of a test light to the glow plug wire.
The other end to ground.
Momentarily turn the key on while watching the test light.
Does it light up?
- Yes, test Glow Plugs.
- No, test Controller, Relay.

*** Pre '87 Controller, Relay test. ***
The relay is attached to the right (passenger) inner fender and has 4 terminals.

1 large terminal (Input Terminal) goes to full time 12v+. (battery)
The other large terminal (Output Terminal) goes to the glow plugs.
1 small terminal (Power Terminal) is controlled 12v+ from the controller. (Purple wire)
The other small terminal (Ground Terminal) goes to ground. (white with black tracer (I think))

Ensure there is 12v+ to the Input Terminal of the relay.
Ensure Ground is good, both the base and Ground Terminal.

Relay test:
1. Attach one end of a test light to ground.
2. The other end to the Output Terminal of the relay.
3. Remove the small purple wire from the glow plug relay Power Terminal.
4. Momentarily apply 12v+ to the Power Terminal on the relay. (where purple wire was)
  Does it light up?
  - Yes, relay MAY BE good.
    - Test voltage at the battery and the Output Terminal on the relay while relay is energized. BE QUICK. (10 seconds or less)
    - Voltages should be close to the same. If not replace relay.
  - No, Relay is not working.
Controller test:
1. Attach one end of a test light to the relay Power Terminal (purple wire, do not remove from relay)
2. The other end to ground.
3. Turn the key on while watching the test light.
  Leave the key on until the test light goes off (or cycles) or 10 seconds which ever occurs first.
  Does it light up?
  - Yes, The controller MAY BE good.
    - Does it go off by itself? (It may cycle, thats good)
      - Yes, Controller is good.
      - No, The controller has FAILED ON ... Replace!
  - No, The controller is bad replace.

-Enjoy
fh : )_~

Aug 25, 2010 | 01:24 AM

Rick Wallace

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Half way? mine never came on unless it was all the way on,are you sure you didnt cross a wire on the new relay?

Aug 25, 2010 | 08:33 AM

mabc926

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Thanks Festus!

And Rick I don't think I did, I had 84_f250_6.9 come out with his truck and we hooked everything up just like it was on his.

Anyways I got a new glow plug relay, gonna go put it on and see if that was it, if I find out that my glow plug controller is bad I'll just hook them up to a push button.

Thanks again guys.