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Old 01-27-2008, 07:13 PM
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Glow Plug Relay 300SD contact points ?

Are there different types of glow plug relays ?

I was changing my glow plugs out on a 1985 300SD(5 in total) and was checking the Glow plug relay.

The glow plug harness had a connector with 5 female "holes" going to each of the glow plugs. The glow plug relay had only 4 contact points(Male) or "prongs" that connected to the glow plug harness (female) connector.

The glow plug harness fit onto the glow plug relay OK. There seemed to be no missing or broken pins on the glow plug relay.
However no voltage was going to the 5th glow plug (ie the "missing" pin)


I have had this car a bit over a year and was changing the glow plugs as the glow plug light went out and several plugs tested open.(Batt ground to connector with 5 female "holes")

Glow plug light now lights and car starts, but...

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Old 01-27-2008, 07:28 PM
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Originally Posted by marybeth View Post
Are there different types of glow plug relays ?

I was changing my glow plugs out on a 1985 300SD(5 in total) and was checking the Glow plug relay.

The glow plug harness had a connector with 5 female "holes" going to each of the glow plugs. This is the glow plug, plug. They're numbered. The glow plug relay had only 4 contact points(Male) or "prongs" that connected to the glow plug harness (female) connector. This is the timer plug.

The glow plug harness fit onto the glow plug relay OK. There seemed to be no missing or broken pins on the glow plug relay.
However no voltage was going to the 5th glow plug (ie the "missing" pin) See above. You're trying to measure plastic.


I have had this car a bit over a year and was changing the glow plugs as the glow plug light went out and several plugs tested open.(Batt ground to connector with 5 female "holes")

Glow plug light now lights and car starts, but...
Good for you on testing the GP's, less than 1 resistance is what you want. Voltage, I think, should be measured on the plugs themselves, vs the plug on the relay.
Pic is of a new relay I have, "just in case!".
The black "pins" are just there so can properly line up the the plugs, only one way fits.
However, the dash light works, the car starts, what's the problem?
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Glow Plug Relay 300SD contact points ?-parts-089.jpg  
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Old 01-27-2008, 07:35 PM
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Originally Posted by marybeth View Post
The glow plug harness had a connector with 5 female "holes" going to each of the glow plugs. The glow plug relay had only 4 contact points(Male) or "prongs" that connected to the glow plug harness (female) connector.
You should have one pin per glow plug. Even the 616 (four cylinder) engine relay had five pins; one just was not used.
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Old 01-27-2008, 07:46 PM
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toomany MBZ -thanks so much for the pic. My Glow plug relay looks the same EXCEPT my glow plug relay has only 4 metal pins, the relay is missing what should be pin #5 to the timer plug (hence no voltage to the 5th glow plug.)

While the car starts and the glow plug light lights-I would like to get the proper relay
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Old 01-28-2008, 05:22 AM
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Originally Posted by marybeth View Post
toomany MBZ -thanks so much for the pic. My Glow plug relay looks the same EXCEPT my glow plug relay has only 4 metal pins, the relay is missing what should be pin #5 to the timer plug (hence no voltage to the 5th glow plug.)

While the car starts and the glow plug light lights-I would like to get the proper relay
I see, and agree. They are pricey tho.
https://www.***************/search/product.aspx?sid=dlidirjkjbzwqp45smyvt155&makeid=800016@Mercedes&modelid=1194049@300SD&year=1985&cid=glow%20plug@glow%20plug&gid=7164@Glow%20Plug%20Kit and you need another GP.
tf007, you're right, the relay in the pic is for 4 or 5 cylinder engines.

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