I have a couple of questions regarding the glow plug relay on my 81 240D. This is due to sometimes the relay doesn't work.

1. I took a look at the fuse on it. It is a metal type of fuse. Is there a newer type of fuse that I should replace it with?

2. If I were to replace it, should I clean the connections again before I install them on the new relay?

3. If I install a new one, is there just the two connections?

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1981 240D
Click Here To See My Mercedes

no, only if it;s really nasty, which i doubt, yes. also, that fuse can crack and not look obvious. BTDT

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Would the relay still work if there was something wrong with the fuse?

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1981 240D
Click Here To See My Mercedes

The strip fuse can (so I hear) be a source of intermittent troubles with this relay. If your strip fuse weren't conducting, your glow system would be dead in the water.

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1984 300D Turbo, 326000 Km, Thistle Green Metallic

Ok, so I should try a new fuse before buying a new relay, right?

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1981 240D
Click Here To See My Mercedes

Oh yes, you should. At the very least, a new fuse will save you the inconvenience of hunting down and testing a relay from a wrecker (or hopefully not buying one new).

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1984 300D Turbo, 326000 Km, Thistle Green Metallic

Were can you buy a fuse like it? Or is it off to the Mercedes-Benz parts place? I never seen a fuse like it before..

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1981 240D
Click Here To See My Mercedes

You can inspect your orignal fuse by removing it. Any defect will be obvious as it is only a calibrated strip of metal. Saves hunting for a fuse if not required.
In my opinion though your problem is more likely to be an old tired glow plug relay. Seek out a hulk at a wreckers for a used one or try one of the used parts from our used parts forum. Those relays get tired with time. Just my experience and you would need to substitute the relay anyways before troubleshooting further if the fuse strip is intact.
The above said at some point of developement of the glow plug circuit on 123s the relay light would not come on if certain glow plugs had failed. So quickly check all your glow plugs for continuity. I do not know what year that started in. Not coming on would be a constant in my opinion. Since yours again is intermittent beg, Borrow, or aquire a cheap relay for a test.

Yep - check the relay operation too. If you find the relay is toast, you can replace it easily. If you know it needs replacing, you can always experiment with rehabilitating the existing relay. I recently opened mine (the original relay, made in 1983) to discover that 25 years of actuation had left of coating of carbon on the main contacts inside. A bit of careful application of sandpaper, and I was back in business. I'm not saying this is the right plan for everyone, but it did work for me and my situation.

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1984 300D Turbo, 326000 Km, Thistle Green Metallic

Well I bought a new relay, has the old one was toast. The old one was made by VDO in Germany. New one is made by Bosch in Malaysia, which won't last as long as the VDO one.

The glow plug light goes out very fast, is there a temp sensor somewhere or is the new one better?

The repair person that I take it to said that the glow plugs are still good, I was thinking of replacing them, since they are original. What do you think?

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1981 240D
Click Here To See My Mercedes

Yes, there is a temp sensor. Can you quantify "very fast" and state the ambient air temperature?


If my glow plugs are 27 years old, I would replace them without hesitation.

It was about 10 seconds and it was 70 outside.
I know I don't want to buy Bosch ones, any good ones?

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1981 240D
Click Here To See My Mercedes

At that temp, ten seconds is a long time.

Because?

I have a 1981 240D and i replaced the relay with a Ford one....eek.....and installed a push button under the dash to warm the glow plugs. Works like a charm.

If you have a push button switch why the relay?

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

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