PRE GLOW TIMER RELAY for 1982 300D HELP ?? plz. - Mercedes-Benz Forum

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post #1 of 5 (permalink) Old 04-14-2005, 10:20 AM Thread Starter
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PRE GLOW TIMER RELAY for 1982 300D HELP ?? plz.


I have an issue with my 1982 300D not starting. It has a brand new battery which when I tested is holding 12V. I tested the posts while disconnected from the car and it shows 12V. However when I jumped the car to get it started - the car runs fine - then when I goto start it again the JUICE is low. The thing is when I drive it around a bit it will start again but once left for a long period something appears to be draining it. Though the Battery still registered 12V.

The thing that is leading me to the PREGLOW TIMER, is when the car is turned off I am getting a fairly loud buzzing sound from that TIMER RELAY. It will buzz until it is barely heard and then seems to shut down. (Basically seems like it buzzes with the car off until it buzzes no more.)

I noticed someone on this forum that had a similar battery problem and someone suggested taking the BIG PLUG off of the Timer Relay and trying to start the car and see if it holds a charge. IS THIS THE BEST THING TO DO FROM MY STANDPOINT ? What do you recommend ? I don't want to buy a timer relay unless I know for sure ($150 part). The battery is brand new, and if jump started the car runs with all electrical elements working radio, lights heater etc ... However when running if I have the heater and lights on at the same time the radio will Dim.

This is all new, ** could it be the alt. belt (like the other fellow found out ?? ) or the Timer Relay that is buzzing unusually ??

Thank you
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post #2 of 5 (permalink) Old 04-14-2005, 06:28 PM
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RE: PRE GLOW TIMER RELAY for 1982 300D HELP ?? plz.

Has your battery discharged at all during the problem? Does the dash battery light come on? If you’re having a charging problem where the belt is loose or the voltage regulator is bad then the battery will at some point discharge, even if it’s new. How often have you jumped the car?

It is possible for the glow plugs to remain on with the engine running, causing a drain – but again, your battery will discharge. A failed glow plug relay may cause this. What if anything is the glow plug dash light doing? Does it go on and then off right away?

Are you sure your battery is remaining charged at all times? If so that is not consistent with the problems you’re describing.

Also, post your question in the w123 forum, lots of experienced folks there to help.
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post #3 of 5 (permalink) Old 04-14-2005, 07:02 PM
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RE: PRE GLOW TIMER RELAY for 1982 300D HELP ?? plz.

Test battery with car running, it should be about 14 volt if there isn't much electrical running. no less than 13 volt or your alternator is bad.

No idea on the buzzing.
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post #4 of 5 (permalink) Old 04-15-2005, 07:44 AM Thread Starter
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RE: PRE GLOW TIMER RELAY for 1982 300D HELP ?? plz.

Thanks for the replies.

Here is what I did last eve.

I went home and jumped the car to get it going.

I unplugged the BIG PLUG on the Glow Timer.

* I had to leave it plugged in to start it because it was so cold last night, and it just would not start without the glow plugs.

Anyway, it started right up, then I disconnected the BIG PLUG with it running. Then I took it for a ride for about 15minutes. Once returning I shut it down, waited a few moments and it started right back up.

Last night I kept the BIG PLUG off the Glow TIMER, then this morning I plugged it back in to see if it would start. GUESS WHAT ? It did.

hmmmm, before it was losing it's charge in a few hours, now it is staying charged all night without the BIG PLUG on the Glow Timer. Also I did not hear that awful buzzing sound this morning either. COULD THE GLOW TIMER HAVE BEEN STUCK ???
I left the BIG PLUG connected when I left this morning and I am going to try to start it again when I get home tonite. Perhaps the problem was solved when I took apart the GLOW TIMER RELAY ? There does seem to be a small spring like mechanism inside the GLOW TIMER, could that have been stuck ??

Anyway, if it continues to lose power with the BIG PLUG on I am wondering if this could be a BAD GLOW TIMER or anything else >? Funny that it stays charged with that BIG PLUG removed. Though I need it plugged in - to start the car cold.

Thank you for your advice, any additional thoughts are appreciated -
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post #5 of 5 (permalink) Old 04-19-2010, 07:57 AM
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Post buzzing when I turn the key & rpm gauge goes all the way over

I'm having a similar problem with my 1983 300D, would run good then wouldn't start, have replaced the starter, battery, glow plugs, belts, would run good for 4 days after each of these "fixes" and then when I turned the key it's buzzing when I turn the key and won't start even with a jump. The battery is fully charged and brand yesterday when under the hood I had my husband turn the key and pinpointed that the buzzing/vibration was coming from the pre glow relay, tapped the side of it and the car started...reading through these posts I'm not sure what we need to do's been really frustrating trying to figure out the problem...he adjusted the valves yesterday as well but has anyone else had this problem...lost the keys a while back and changed out the ignition switch and it seems like I've had problems since then, could it be something in the switch??? Also it doesn't always turn off but it's not the vacuum pump...sometimes it does sometimes it doesn't and I have to hit the :"stop" button under the hood. I also read that there is a glow plus relay fuse?

Please anyone, I could use some help...
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