My 190D is having more glow plug issues. First it was bad plugs, so I replaced them all with Bosch Duraterm, then a bad battery, replaced that with a Mercedes OEM battery, then had connection issues from corrosion causing the fuse to go so I cleaned the contacts and replaced the fuse but recently, the glow light will not come on. I tested if the bulb was bad and it is not. I don't really know what it could be. I am having no issues at all with the glow plugs besides the light.

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.

The light works off of an internal temp sensor on My Year and Model. I suppose if that is not working the Light is not going to function properly.

Even after reading the Manual and the various threads I don't undersatnd how the troubleshooting function of the light is supposed to work. I only know if the light is wonky to check the Glow Plugs first.

Also did you ream or otherwise clean out the Glow Plug Holes?


It would be nice if someone local had a Spare Glow Plug Relay to swap and see if that fixes it.

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84 300D, 82 Volvo 244Gl Diesel

Yes, I reamed the holes when I replaced the glow plugs, carbon wasn't bad at all when I did it. Could be that the sensor (is that the one under the glow plugs on the GP harness?) could be disconnected or the harness is damaged.

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.

I don't know what the set-up is on a 190D. My 84 300D has the temp sensor inside of the Relay.
I have never read of anyone finding a way to test the temp sensor so it has never been identified as the cause any problems.


These are the Wires on My Glow Plug RelaySquare Glow Plug Connector, what wires go to it.
#1 Red Wire with White Stripe, Run Start Input

#2 Violet (Purple) Connects to the Starter Solenoid Wire (On Turbo Models at the Terminal Block in front of the Battery) allows Glow Plugs to be on during cranking.

#3 Blue Wire with White Stripe, Goes to the Glow Plug Light. The Voltage comes from the Relay through the Light and to a Ground (I can't remember where I got the Voltage path info. If it is correct if you apply + Voltage to the #3 Termnal your Glow Plug Light should turn on. That would test that circuit from the Plug to the Light and I guess the Light is grounded in the Instrument Cluster.).


#4 Brown Wire, Goes to ground.

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84 300D, 82 Volvo 244Gl Diesel