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  #16  
Old 11-07-2010, 03:32 PM
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Light only goes on when I put it on drive and hit the pedal. Then it doesn't turn off until I shut down. I tried swapping another relay in and it does the same thing. So the source can't be the relay.

I just drove 200miles to PA wilkes barre and had no problems. Car starts up without any problems. Even when cold. Driving back to NYC tomorrow

Biodiesel300TD Where exactly are these sensors?

digi

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  #17  
Old 11-07-2010, 07:02 PM
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Here (pic w/ 2 arrow) is where the two sensors are in my 78 240D. Your's may not be in the exact same location, but they will be on the same side of the head as the glow plugs.
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Glow plug light on when driving-temp_sensors.jpg  
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  #18  
Old 11-07-2010, 08:29 PM
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Since the subject car is an 84 I believe that of the two sensors located on the head, one is for the temp gauge and the other is for the aux fan "fast" speed, for engine cooling (120C cut-in, I think).

This is how it was explained once to me on my 85.

Please correct me if need be.
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  #19  
Old 11-07-2010, 09:09 PM
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Quote:
Originally Posted by micalk View Post
The relay is the most likely source. The relay applies 12V to the light.
Quote:
Originally Posted by tangofox007 View Post
The relay only powers the glow plugs. If the relay also powered the indicator lamp, the lamp would remain illuminated for the duration of the glow cycle.
If you want to play semantics here, fine. The schematics call the entire assembly a "Glow Plug Control Relay". You can say that the "relay" doesn't control the light, but that light is turned on by the assembly. And like I said, MB calls the assembly a relay. And why not let everybody know what is applicable instead of saying what isn't. Gasoline isn't applicable here either but saying so doesn't help anybody.

Digi-

If you feel adventurous, disassemble the 4-pin connector and pull socket #3 out of the connector. If the light still comes on, the problem is probably in the dash. You need the other three connections for the relay assembly to operate properly. Since two relay assemblies are displaying the same symptoms, doubt that it's the relay.

The temp sensor is built into the relay for your model, so there isn't a connection for temperature to the engine. I think its only function is to determine how long to illuminate the dash light. There are other temp sensors in the head - temp guage and climate control lockout come to mind immediately - but neither has anything to do with the GPs.
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  #20  
Old 11-07-2010, 11:44 PM
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See if a temporary external ground to the relay helps. I am far from certain about this.
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  #21  
Old 05-22-2011, 06:25 PM
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I'm revisiting this. I spent all winter with the glow plug light on. Yes it cycles on and off when I turn the key. Once it's off, it doesn't turn on until I put the car in drive and hit the gas. Then it stays on until I shut the car off.

I tried "If you have a 20 amp scale on your DVM it's very easy. Unplug the connector from the glow plug relay. Connect one lead of your DVM set to 20 amps) to battery + terminal post. Connect the other lead of your DVM to one of the 5 terminals of the glow plug harness connector you unplugged. It should surge to around 18 amps and then drop slowly to around 12 amps."

I also check my relay. It's fine.

I checked both sensors on my block and they're both plugged in.

What else can it be? It's worth noting that this started happening right after I changed my glow plugs a while back.

digi
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  #22  
Old 05-23-2011, 12:22 PM
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Check the resistance of each glow plug at the relay plug. Good plugs will read about 0.7 ohms. It is possible for a glow plug to be bad out of the box or for one to quickly burn out depending on what brand you used.
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  #23  
Old 05-23-2011, 12:55 PM
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Thank you! All glow plugs read .07 except for number 4. It reads 1.57. Does that mean 4 is bad?

Here's a dumb question... which glow plug is 4. Do you count them from front to back?
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  #24  
Old 05-23-2011, 03:18 PM
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Quote:
Originally Posted by digieditny View Post
.......................

I tried "If you have a 20 amp scale on your DVM it's very easy. Unplug the connector from the glow plug relay. Connect one lead of your DVM set to 20 amps) to battery + terminal post. Connect the other lead of your DVM to one of the 5 terminals of the glow plug harness connector you unplugged. It should surge to around 18 amps and then drop slowly to around 12 amps."
.........
What were the results? This is a much better test than the resistance test since this heats the glow plugs up and measure actual current consumption. The glow plug light is not on the same circuit as the glow plugs. If your glow plugs were actually on all the time while you drive, they would have burned out long ago.
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  #25  
Old 05-23-2011, 03:28 PM
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Hey Funola. All plugs read 12amps. I did not see a surge though.
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  #26  
Old 05-23-2011, 04:25 PM
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Quote:
Originally Posted by digieditny View Post
Hey Funola. All plugs read 12amps. I did not see a surge though.
The "surge" is seen immediately after you connect the ammeter, should be around 18 amps, then graduallydrop to about 10 amps as the plug heats up fully.
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  #27  
Old 05-24-2011, 10:12 AM
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Quote:
Originally Posted by digieditny View Post
Thank you! All glow plugs read .07 except for number 4. It reads 1.57. Does that mean 4 is bad?

Here's a dumb question... which glow plug is 4. Do you count them from front to back?
Assuming the reading is accurate and if it was mine, I'd swap in a known good glow plug and see if that fixes things.
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'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
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  #28  
Old 05-24-2011, 12:00 PM
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Yep. that's what I'm going to do. I don't have any more spare glow plugs. I'm gonna have to order them. Hate that I live in one of the biggest cities in the world and I can't find one locally. Annoying.
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  #29  
Old 06-06-2011, 01:36 PM
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Ok changed Glowplug that was bad. Now the light is still on... I checked the glow plugs 3 times. They're fine... Checked relay and it was fine.

Here's what I did next... I drove the car until the GP light lit up. Then I stopped the car and unplugged the relay. The light STAYS on. So I believe that means 1 of 2 things... it's some kind of short in the dash OR maybe that the bulb belongs to either the ABS or seat belt light. Does a 1984 euro 300td even have ABS? IS there something I can unplug that turns off the ABS light to test if that's it or not?

The right side of dash has a spot for seat belt, ABS and glow plugs.

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