Mercedes 240D won't start, Glow plug relay? - Mercedes-Benz Forum

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post #1 of 6 (permalink) Old 07-21-2014, 02:48 PM Thread Starter
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Mercedes 240D won't start, Glow plug relay?

Hi, I apologize if this issue has been addressed. I'm new here and was unable to find anything specifically to my problem.

I'm using a friend's '78 240D while he's out of the country. I've been driving it for about a month and it has run great. I went to start it this last week and turned on the glow plug. I walked away for a minute to put something in the trunk and there was smoke coming thru the dash vents. I quickly turned the plug off and found the relay box and blade had melted and fused together (see first picture).

I am not mechanically knowledgable and after reading more about it and speaking with the owner, I realized the relay fuse was not even in the plastic box to begin with. Also, that "it was already semi-melted together" according to my friend. Maybe it contacted some metal and shorted when I tried to start it? In any event, I disassembled and cut away all the melted plastic from the blade fuse and wires. I then reassembled (without the box as it was destroyed) to see if the glow plug would work. It lights up and I can hear it as normal, but when it switches off and I turn the ignition to start the car, there is only a click sound. Sometimes several faint clicks. The blade fuse is intact albeit damaged looking. It doesn't seem like the problem lies here although I have read that a blade fuse with even a hairline crack or any damage can fail. The connecting wires are in fine condition, and like I said the glow plug does come on and it sounds normal as it's doing it's thing so seems like the relay is working. I was considering buying a new blade fuse and box just to see if it would effect the problem, but it just seems like it is something else to do with the charging system. But it has to be related to the relay box burnout.

Is any of this familiar to anyone? Maybe the relay problem caused a failure somewhere else? Thanks for any help. I can take more pictures if you like. And all fuses in the central box are good.
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post #2 of 6 (permalink) Old 07-22-2014, 02:03 PM
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You say after the glow plug light goes off when you try to start the car you hear one or several faint clicks?

That sounds like a dying battery - perhaps just low on charge because of all the energy to melt the box.

First thing is to secure the relay and fuse wires such that they cannot short out to anything. You should replace the cover and figure out why it would melt. Could be a bad relay.

But then it sounds like it will start once you charge the battery (you might need to replace it but I'd try a recharge first)

Good luck

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post #3 of 6 (permalink) Old 07-24-2014, 11:54 AM Thread Starter
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Thank you for your reply. Since, I have tried to jump the 240D with no different results. The glow plug still turns on, goes off. I try to turn the car over and...nothing. "click". Usually just once and then every attempt after, there is absolutely nothing.

I have headlights operational, inside warning lights are on. I've also started to consider that, if the blade and box were already melted, that maybe it was something else that was causing smoke. I don't really see, if the box was melting and causing smoke how it would get through the engine firewall and up through the dash vents anyway, but maybe I'm wrong.

The relay is under the steering column isn't it? Would the glow plug still be working though if it was bad?

According to this video, his relay is bad and the glow light won't come on...but mine does.
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post #4 of 6 (permalink) Old 07-24-2014, 01:41 PM Thread Starter
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Battery checks out good with a volt meter
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post #5 of 6 (permalink) Old 07-28-2014, 07:12 AM
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Take battery to store and do draw down test. also take starter there and get tested.
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post #6 of 6 (permalink) Old 07-28-2014, 03:24 PM
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can you send a picture of the glow plugs arrangement , that show the bar connections .it is not normal for the fuse box to melt like that . a shorted number 4 glow plug will do that .see if car cranks with glow plug wire disconnected .
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