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1988 560 SL
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81 Posts
Discussion Starter #1
When I start the car, the glow plug light does not go out until the motor starts. I use the red seat belt indicator light as a "timing" guide that the plugs are hot. It starts right up ,even on cold days.
Any suggestions.
Thanks,
 

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1959 220S cabriolet, 1983 240D original owner, 1999 E300 turbo diesel, 1988 560SL, 2003 SLK320
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3,513 Posts
Test the plugs with an ohm meter. Good plugs will read 0.6 ohms.

Len
 

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1988 560 SL
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81 Posts
Discussion Starter #3
Thanks, I will test the glow plugs. I guess because it starts even when it's cold (13 degrees this morning) without being plugged in, I ruled that out earlier. Thanks again for your advice.
John
 

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1959 220S cabriolet, 1983 240D original owner, 1999 E300 turbo diesel, 1988 560SL, 2003 SLK320
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3,513 Posts
Glow plugs are often the problem and they are so easy to test. If they test out okay, then move on to the next likely candidate.

Len
 

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85 300cd, 2000 ford excursion diesel, 1999 528 itwagon 95 roadking
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371 Posts
check the glow plug controller, its on the drivers fender about midway towards the headlites, usually the lite goes on when there is a problem with 1 or more glowplugs. pull them and make sure there are healthy. apply power to the end with an nut and ground the body and be carefull, the plug should start to smoke from the part below the nut that you used to unscrew it and count to 5 and it should be red hot. also make sure you pull them and put them in order of cylinder, they should be full lenth if they look melted, you have a leaking injector in that cylinder.
 

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Apologies for jumping into this thread - I've had a similar problem with my '83 240D. My glow plug indicator light just stopped coming on - a resistance check shows no open circuit on the plugs, so I'm wondering if the switch has gone south on me.

Again, my apologies for butting in on the thread - and thanks for any advice on troubleshooting this.
 

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1959 220S cabriolet, 1983 240D original owner, 1999 E300 turbo diesel, 1988 560SL, 2003 SLK320
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3,513 Posts
Pull the 80A strip fuse out and replace it if you can. If it doesn't fall apart in your hand, go ahead and replace it if you don't have a spare. If the plugs are fine and the fuse is fine, I'd guess you likely have a bad glow plug relay.

Len
 

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1988 560 SL
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81 Posts
Discussion Starter #8
Would a battery on it's way to perdition have an effect on the glow plug light? My light works properly only once in a while.I have no problem starting the car and everything tests ok.
 

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1959 220S cabriolet, 1983 240D original owner, 1999 E300 turbo diesel, 1988 560SL, 2003 SLK320
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3,513 Posts
If your battery is more than five years old, could be time to replace it anyway. You can always have your battery tested for free too. Or try a known good battery.

Len
 

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Hi Len,
Thanks for the advice - I did check the fuse but it looks fine. I'll have to dig a little deeper to see where the problem is. Any thoughts on whether it's a good idea to buy used relay off e-bay? (I'm a compulsive skinflint - but, through bitter experience, have learned cheaper isn't necessarily better...)
Many thanks.
DT
 

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W-1-2-3 Go!
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16,161 Posts
My glow plug light didn't turn on today. Is this a sign that the bulb is out? The car starts strong first try from cold engine. Strip fuse on gp relay is intact. I'll contact my mechanic tomorrow, I remembered we had a small chat about this while he was finishing installing my alternator & belts.

If I remember, a flashing glow plug light means a glow plug is gone, right? Or perhaps the relay? But one that doesn't light up even when engine is on means bulb is out, correct?

Just making sure before I dive under the dash and push out the cluster. Might as well remove it while I'm at it, and install the rheostat I've been waiting to take out the box. Thanks
 

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1975 200 (sold); 1978 200 (sold); 1979 300TD (sold); 1985 230E
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122 Posts
i have the same problem as yours karugs.. light doesnt come on.. but car starts fine... even on cold nights or early mornign starts...

pulled the plugs out and tested them.. they all glow fast... fuse bar is ok... next step is the heater relay.. havent gone to checking that out yet though.. hehehe..:p
 

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W-1-2-3 Go!
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Heater relay? I don't see why it would be connected... [?] I'd go for the bulb first. Seems most logical since car starts good and has no starting problems. And maybe it's just me but coincidence dictates that my mechanic just talked to me about this. Flashing would be a warning that a GP or fuse is going bad. Sudden non-working GP preglow light means it is bulb. Only one way to find out... [:p]
 

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1975 200 (sold); 1978 200 (sold); 1979 300TD (sold); 1985 230E
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122 Posts
bulb checks out fine.. transfered the bulb to another socket.. lights well enough... line to the bulb works fine... it just doesnt turn on...
 

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1975 200 (sold); 1978 200 (sold); 1979 300TD (sold); 1985 230E
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122 Posts
hehehe.. get the cluster out?..easy enough.. you can do it.. heheh. keep us posted on what you found out..:D

i'm still stumped as to what's causing my non-lighting glowplug indicator...:D
 

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1982 300CD
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5,134 Posts
So, my light stopped working yesterday. But it stopped, then worked once more, now nothing. Should I be looking at the bulb, or is there a relay, or wire connection that typically goes bad? Anyone find anything out?
 

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1983 240D 4 speed
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102 Posts
I had a problem with intermitant glow plug lights coming on sometimes and not at other times.
Then the alternator went.I replaced the altrenator with a "new" rebuild and since have not had any intermittant glow ligh problems. Maybe have your alternator/voltage regulator checked ?
 

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1988 560 SL
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81 Posts
Discussion Starter #19
I continue to have a problem with my glow light but after 5,000 miles it keeps starting right up so I've decided to live with it. I tried to repair it but to no avail.
 
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