In mine, the GP relay glowing process would have to be recycled two - three times before the bulb would illuminate. It started as if it had a few weak plugs, too.

All plugs checked out perfect, the strip fuse was fine. I removed the timer plug, the relay plug and sprayed female and male contact points with WD40. No difference.

Next, I disconnected the battery and removed the live red wire behind the timer plug and sprayed WD40 on the contact screw and connector.
Problem solved.

I just tried this with no luck.

My battery is reading under the 12.5 volts that dieselgiant lists as the necessary minimum for the glow plugs to work. So, with my battery under that voltage, would the dash light not light up?

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1982 Silver 300DT

I think the light will come on, just not enough juice to turn over, repeatedly. The SD's battery is not strong, grinding down starter slowes it, yet light comes on as normal. Gotta be mucho power to turn over these 21.5 to 1 compression monsters. New starter will be here Tuesday.

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83 SD

84 CD

Ok. well, time to switch on the Ohm meter and test the relay, wires and plugs.
Little one is waking from a nice nap, so it will have to be tomorrow...

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1982 Silver 300DT

Unitl you get the glow system sorted, try to avoid cranking the engine. Everytime the engine turns, raw diesel fuel is filling the cylinders, and that is going to make it harder to start when you do get the glowplugs working.

Wellll, it seems wierd that you have to put the black cord/pin of the multimeter on the negative pin of the battery. That's a helluva stretch for my itty-bitty cord (er, wait).
At any rate, I put the neg on the neg pole of the battery and the positive in each pin hole of the plug on the glow plug relay. It was on ohms and each time it pegged to the 0.
What am I doing wrong?
Thanks for your patience for the Captain of the casual mechanics!

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1982 Silver 300DT

does your car have a strip fuse?? replace it.

put the battery on trickle charge. You need a full charge to crank well.

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

By 'strip fuse', I think you mean the 80 amp fuse secured by 2 screws. No, I have not replaced that. It's super shiny and new looking.

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1982 Silver 300DT

See if voltage is getting to glow plugs.....Make sure battery is good and charged.....Meter set on DC volts...at least on the 20 volt scale on the meter....ground the black negative meter lead to the head ...positive red meter lead to any glow plug nut that secures the feed wire to the plug..... Have someone start the glow cycle and see what voltage appears on your meter and for how long....My 240D has glow voltage on the plugs for 45 to 60 seconds before the relay turns off ....Ignore the light for now...It can be a source of infinite confusion...my light only comes on for about 8 seconds before it shuts off but the voltage is on the plugs for up to a minute on a cold start....

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1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)

I use the cap of the PS unit as the ground. Have not checked voltage.

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83 SD

84 CD

Actually, you're not doing anything wrong. The "normal" resistance for the glow plugs is about 1 ohm when cold. Your meter probably won't be able to read accurately down to this level, so, it appears that the resistance is "zero". This tells you that none of the glow plugs are open (burned out).

It does not tell you if any of them are weak, however.

I would suspect that the relay is intermittent. Sometimes it closes and applies 12V to the plugs........sometimes it doesn't. This is also characteristic of a bad fuse, however.

You'll need to check for voltage at the glow plugs when you cycle the key as Kevin suggested above.

4 of the 5 glow plugs were dead.
Now it runs fine.
Go figure.

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1982 Silver 300DT

it's also a bit warmer out...
still weird that it was simultaneous with the sunroof repair.
these cars are a joy aint they?
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Just curious how you determined they were dead and what brand were they?...Thanks for the follow up post....I was wondering if you had got it running ok....

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1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)