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our '82 300 SD still wont start. when the key is turned to pre start the glow plug light on the dash does not come on at all, but i am getting 11.37 volts exactly at all 5 glow plugs for around 20-25 seconds. is it fair to assume that the relay is working properly? however, when i disconnect the 5-pin plug from the relay (that runs from the relay to the glow plugs) the the glow plug light on the dash works properly (obviously, the glow plugs do not). could this be related to the not starting problem or should i ignore it? i am going to change out the fuel filters and bleed the fuel system for air. is there something else i should be doing but am overlooking?
 

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You should check the glow plugs by their resistance values. Ideally, checking them individually will eliminate other sources of error. Another way is to ground the meter and probe each wire to its respective glow plug.

Normal resistance (at least for my 602&603 engines) is .5 to .7 Ohms, but a value of 2.0 can still be good.

For a problem of the light not coming on at all, glow plug #1 alone could be the culprit, or any other two. This is of course in addition to the possibility of a bad relay, for which the only test I have found thus far is switching with a known good relay.
 

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yeah stevano, I am waiting for you to try a new glow plug relay (they are not terribly cheap, but not terribly expensive) and posting that it solved the problem.

I would hate to steer someone into buying a part that they don't need, but I would bet 10 to 1 that you have a bad glow plug relay based on all of your posts.
 

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Glad you got it fixed! Dang...sometimes it's the simple things. Thanks for the follow-up.
 
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