All of a sudden the glow plug light began to blink after the car is started. It blinks for maybe one minute and then stops.

Otherwise everything acts normally. The car starts fine.

It's a 1980 300D.

What could this be? The factory shop manual lists all kinds of troubleshooting problems that occur with the relay, but it doesn't mention this.

Richard

At least one of your glowplugs is burned out or close to it.

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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

Does the W123 really have the blinking light for bad plugs? I mean, his is obviously blinking...but mine was not when I had a bad plug on my '85. I was under the impression that when enough plugs went out on the later style W123 setup the light simply wouldn't light.

Slightly confused as to this. I thought the blinking was a post-W123 thing.

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1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

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Visit the W123 page on iFixit for over 70 helpful DIY guides!

Check the Glow Plugs with an Ohm Meter (don't recommend buying Parts there) go to the Diesel Giant Site under Glow Plug Repair and there is a pictorial on how to check with the Ohm Meter.

Check the Strip Fuse on the Glow Plug Relay for a crack; the crack can be hard to see (this happend to me). Check the Screws that hold it down to see if they are loose.

The Engine will start with one bad Glow Plug. After it starts does it sould like there is one Injector that is more noisy?

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84 300D, 82 Volvo 244Gl Diesel

I had the same issue a couple years ago. After checking all the glow plugs it turned out that the glow plug relay had gone bad.............

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2012 Mercedes ML350 Bluetec 102K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 238K (mine)
1998 Volvo S70 T5 Turbo 211K (kids)
1994 Ford F150 4WD 246K (firewood hauler)
1983 Mercedes 300D 384K (diesel commuter)

Sounds like you may have a GP relay from another car. Blinking light indicates a short. How is your car starting?

My w116 300sd (1979) glow plug light blinked when I had defective plug(s), I know because it happened just after I got it and it was my first diesel. It scared the wits out of me.... So I was going by that (same relay style as my 1980 wagon, so I assumed same for his car?).

Now that I think on it, am pretty sure my wagon blinked its light at me at one point too.

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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

The car starts perfectly. Instantaneously. Couldn't ask for better. Of course I live where it is eternal summer.

I have a set of new glow plugs and a reamer but with the car starting like this I am not at all motivated to install them.

Richard

It could also be a short in the glow plug ground circuit.

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1983 300SD
1988 420SEL