The preglow light didn't come on and from the way it "tried" to start, the preglow isn't working.
The relay fuse looks intact.
After removing terminals and inspecting the relay, including a general wiggling of the wires )...... The preglow light flashed once before going out.
Should I get out my multimeter and start testing the relay? then then the glowplugs?
The relay is less than two years old.
Please advise.
Thanks in advance.

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Wordmanjay
Tribetown, Ohio

Check the pins of the relay. Do they appear to have any corrosion? I used a brass brush on the pins (lightly) and now it works every time.

I'm thinking a very light coating of silicone, dielectric grease may help eliminate future problems.

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Sam

84 300SD 350K+ miles ( Blue Belle )

how old are the glow plugs?
If memory serves when one goes
bad the glow light won't come on but
the rest of them will work fine.

Maybe you have one or more bad GP's

Louis.

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Not always the smartest but certainly not dumb?

Check that when the key is turned to the preglow position you have power at the terminal at the lower left of the small plug on top of the relay (lower left with you looking at the business end of the plug). Sorry I forget the pin number. That will tell you if the signal is getting to the relay from the ignition switch.

With a test light or OHM meter with a 12v setting, check if you are getting power to the plugs when in the preglow position. You will see around 11v at the plugs if things are okay with the relay.

For both those tests, make sure to use a good ground -- battery neg terminal if possible. Also make sure your battery is fully charged. I have been told that a weak battery will cause symptoms such as yours. If you see less than 10.5v at the plugs, charge up the battery, clean the main ground (neg cable attachment to inner fender) and try again.

If the plugs are more than two years old (assuming Bosch/Beru brand installed), one or more may be burned out. If other brands, people have reported plugs failing in as little as a few months.

One simple thing you can try is to gently tap the side of the relay with the ignition at the preglow position. Or press down on the two plugs on top. Sometimes the relays stick when the temperature drops -- though this is something I would expect on a relay much older than two years.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

He is correct I had two bad glow plugs and the light did not come out after replacing the 2 bad glow plugs the light comes out and the cars starts fine

Just a note that it's generally a good practice to replace all the glowplugs at once and save future headaches, if one or two have gone bad or very weak.

I understand in Cali that probably isn't a great concern unless you are up in the mountains like a friend of mine, but in Ohio it would likely be a sound idea given how cold it gets.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

It was the relay. Thank God I had one from my parts car.
Put it in, they pre-glowed and it started.
No problems since.
The relay I replaced wasn't that old. Makes me wonder.

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Wordmanjay
Tribetown, Ohio

What brand of relay was it?

Did you try tapping on it or jiggling the connections (the two plugs), before you delcared it dead?

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

It takes 1 min to check the glowplugs with a multimeter (free w/ HF coupon). I do that routinely at least once per year, and I often find a dead one or two (usually Bosch, but I haven't tracked carefully). I recall a Youtube video. As I recall, you must have 3 bad glow plugs before the lamp won't light. At that point, you will definitely notice hard starting.