Hi guys,
I have a 300d w123. I just changed the glow plug relay, my old one the actually relay had the copper contact points corroded to no tomorrow. The timer and everything circuit wise was still fine but the actual relay contact was CRAP. Anyways, I put a used replacement in today. It works fine but turns off the glow after about 3 seconds in cold weather where the old one glowed for about 10 seconds. This cannot be right can it? It's gotta glow longer than 3 seconds right?

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-E300d '99 350k
-Suburban '93 220k
-TDI Jetta '03 350k
Sold
-F250 '96 7.3
-Dodge Ram 12V
-E320 '95 200k
-E320 Wagon 1994 155k
-300d Turbo '87 187k miles
-E320 1994 200k
-300d Turbo '84 245k (sold to Dan62)
-300d Turbo '84 180k
-300sd '80 300k
-7.3 Powerstroke Diesel 15P Van 500k+ miles
-190d '89 Non Turbo 2.5 5cyl 240k (my first MB)
Tom's Imports of Columbia MO Ruined the IP in changing leaky delivery valve O-Rings - Refused to stand behind his work. Mid-MO MB drivers-AVOID Tom's.

The light means nothing...

Turn off the radio, the blower, everything that makes noise.
Turn on the dome light.
Turn the key to glow while watching the dome light. It will dim when the glow plugs go on.
After about 30 seconds you will hear a thunk/click from the engine compartment. It is the glow plug relay deenergizing. The dome light will get brighter at the exact same time.
That is a full glow cycle.

-Jim

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1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.

If it was not much of a complex soldering job you could perhaps install the relay from your newer aquisition into your old unit. I have never had a glow plug controller from a mercedes apart to know how feasable it is. As one gentleman suggested you may still have your total glow time available and the light is just responding to a faster time constant internally on that particular function of the controller.

JaDavis has a good point, just started doing this, better, yet had to get a jump this morn. Taking in "good" MB {CD} tonight.

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83 SD

84 CD

In my case, after the thunk/click, the batt light gets just a tad brighter about 5 sec. later. That's what I count as the full cycle.
I'm not sure if there is any real difference, but I figure it gives just a little more time for the heat energy to spread a little further, making the start better.

__________________
85' 300D No inspection, No registration fees, Cheap insurance
"If my calculations are correct, when this baby hits 88 miles per hour, you're going to see some serious %$&^."

HEy Yeah you're right... It's still glowing but the light is going out in 3 seconds. So thats it. Anyways, I wonder why the new relay turns the glow light out so quick.

__________________
-E300d '99 350k
-Suburban '93 220k
-TDI Jetta '03 350k
Sold
-F250 '96 7.3
-Dodge Ram 12V
-E320 '95 200k
-E320 Wagon 1994 155k
-300d Turbo '87 187k miles
-E320 1994 200k
-300d Turbo '84 245k (sold to Dan62)
-300d Turbo '84 180k
-300sd '80 300k
-7.3 Powerstroke Diesel 15P Van 500k+ miles
-190d '89 Non Turbo 2.5 5cyl 240k (my first MB)
Tom's Imports of Columbia MO Ruined the IP in changing leaky delivery valve O-Rings - Refused to stand behind his work. Mid-MO MB drivers-AVOID Tom's.