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.
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.
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.
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.
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...)
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
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... 
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?
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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