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  #1  
Old 08-23-2008, 11:47 AM
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Question Interesting problem: glow plug works, but dash light doesn't (with a good bulb)

The instrument cluster light for my glow plug indicator stopped working, but the problem is not the bulb (I've swapped a good bulb in and then verified it was still working after trying), or the glow plugs themselves - they work.

Anyone ever encountered this problem? Is there a typical loose connection?

This is on the 85' 300SD with 152K.

Thanks

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Old 08-23-2008, 01:14 PM
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I had it on both my Benz's and swapping the controller isn't the answer. Honestly I forget what IS the answer because for the trouble of it I just ended up wiring the indicator light right to the glow plugs themselves.

Someone correct me if I'm wrong but there's a separate piece besides the GPC that "calculates" how long to glow based on how cold it is. This doesn't stop the actually glowing but rather how long the indicator light is on. Like a dummy manual for dummy lights.

Hope that helps,
Bill
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Old 08-23-2008, 03:55 PM
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Quote:
Originally Posted by Bill()C View Post
I just ended up wiring the indicator light right to the glow plugs themselves.
What useful information does that provide?

Quote:
Originally Posted by Bill()C View Post
Someone correct me if I'm wrong but there's a separate piece besides the GPC that "calculates" how long to glow based on how cold it is.
No.
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Old 08-23-2008, 03:56 PM
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Originally Posted by pwogaman View Post
...or the glow plugs themselves - they work.
Each and every one?
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Old 08-23-2008, 03:58 PM
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Originally Posted by tangofox007 View Post
Each and every one?
That's the question.

If the lamp does not come on when you turn the key to position 2 but the lamp itself is good, you likely have at least one bad glow plug. This is how the relay informs you.
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Old 08-23-2008, 04:11 PM
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Quote:
Originally Posted by Matt L View Post
That's the question.

If the lamp does not come on when you turn the key to position 2 but the lamp itself is good, you likely have at least one bad glow plug. This is how the relay informs you.
Ah Ha! I'll have to trouble shoot all the plugs now to see if one is bad. Many thanks! BTW, how do I trouble shoot the plugs?
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Old 08-23-2008, 06:53 PM
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If the glow plugs turn out OK, you may also want to check the traces on the circuit board that makes up the back side of the left hand panel of the instrument cluster. Mine had one burned out trace - the light was really dim until I fixed it by soldering a wire in place of the bad trace.
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Old 08-23-2008, 07:09 PM
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Quote:
Originally Posted by OldPokey View Post
If the glow plugs turn out OK, you may also want to check the traces on the circuit board that makes up the back side of the left hand panel of the instrument cluster. Mine had one burned out trace - the light was really dim until I fixed it by soldering a wire in place of the bad trace.
For me this is one of those things that I just ignore. (Perhaps my situation is different)

My light goes on for about 3 seconds. But I know the glow plugs are on as I can hear the CLUNK of the plug relay about 15 seconds or so later.

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