I've been getting a very intermittent no glow plug light in the cluster with hard starting. To help with troubleshooting, I have rigged up a light bulb to the violet wire at the glow relay connector and another bulb at one of the glow plugs so when the problem occurs, I can pop the hood and immediately see what's going on. Since I've rigged it, the problem has not occurred lol.

Anyway, this is how my 85 behaves:

key on - both bulbs on (voltage at violet wire and glow plugs)

turn key to crank starter- both bulbs on (voltage at violet wire and glow plugs)

release key, engine started- violet wire bulb on, glow plug bulb off.

Is this how yours behave? Please state year/ model.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

You've scared it. Consider it fixed .

My glow plug light (1982 300SD) behaves the same way, but I don't know about the violet light. I can try that during the week and see what I get.

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"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

Have you checked that your battery is healthy? On my '85 w123 found that the original relay (that is, original part number) was sensitive to voltage drop and that manifested through intermittent no-glow. (Two different relays did the same thing.)

I found the later, 'universal' relay (w126/w123/w201), slightly smaller with a different part number, worked just fine with a weak battery.

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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

I was not referring to the glow plug light in the cluster, but a test light hooked up across a glow plug.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Battery is good. Ctanking rpm is up there (around 155).

From what I remember reading, the glow plugs are suppose tostay on for a bit after the engine has started. My 85 certainly does not do that.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I think you need the afterglow kit for the plugs to stay on after starting. I have my 85 out on loan, so I'm not much good right now for actual help.