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Old 10-20-2004, 08:19 AM
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Join Date: Oct 2004
Location: Williamsburg, VA
Posts: 108
85 W123 (300 TD) Glow Plug Heater relay

All;

In addition to the relay mounted in the engine compartment, is there a secondary relay located behind the dash that controls the pre-heat indicator light mounted on the dash?

Past several colder mornings (40 degrees, but hey, it's Virginia) shortly after startup, I would hear what sounded like a relay chattering or an electrical short coming from behind the center console in my '85 300TD. After just a minute or two it would quiet, and then no re-occurence until the following morning.

Attempted to remove the center console this past Sunday, but the Haynes manual led me astray (or I failed to pull hard enough). I was able to remove all switches, heater control assy, radio, etc. so I could see back in there. It didn't appear that there were any relays back there, though there are four small metal cans approximately 1 cm. on a side back behind the heater assy. Started the car, no out of the ordinary noises (but it was warm that afternoon)

Now the glow-plug dash indicator fails to come on when the key is placed in the II position, but the glow plugs appear to be pre-heating because the car is quickly starting. Hasn't gotten back into the 40's, and I've not heard the sounds since Monday when I noticed the pre-heat light is no longer on upon start-up (it did chatter/buzz first thing that morning however).

Just coincidence, and the dash indicator bulb has burned out, or is something else going on?

... and speaking of bulbs, are Osram 2721's the right fit for all the bulbs used for center cosole illumination? I'd read stories that some bulbs are to be avoided; too hot, and prone to melting holders, etc. Is it also a 2721 in the glow-plug heater indicator on the dash (I want to have what I need on hand before I tear into the instrument cluster).

Thanks in advance

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Old 10-20-2004, 09:41 AM
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Join Date: May 2002
Location: Charlottesville, VA
Posts: 548
Hi there-

I just replaced the glow plug relay on my 84 TD last night. Wow, what a difference. To my knowledge, only the earlier 123 chassis cars had the relay behind/below the glove box in the interior- our later cars have it in the engine compartment at the front driver's side wheel arch. I don't think there is an additional piece in the interior, for the glow plugs. The sound you are hearing (which I hear in mine, when turning the key to try to get the glow plugs working before I replaced the relay) I always thought was related to the climate control system.

Cheers,

JAS

ps- Where in VA are you?
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Old 10-21-2004, 07:06 AM
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Join Date: Oct 2004
Location: Williamsburg, VA
Posts: 108
jas2wa;

Thank you for the feedback. A bit cooler this morning, and no unusual noises coming from the dash. Of course, I am still not getting the indicator light on the dash to tell me the plugs have finished their pre-heat, but the car is starting quickly.

Need to find time to pull the instrument cluster to check the health of the bulb itself.

You asked about location; I'm in the Williamsburg area. We were out your way last weekend to visit Monticello (along with most all of the state based on the 2+ hour wait time to get in to the house).
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Old 10-21-2004, 08:21 AM
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Join Date: Jul 2003
Location: Charlestown, NH
Posts: 1,008
Not on the relay issue . . . during the initial starting procedure of my '87 300TD I hear a noise eminating from approximately the center of the dash. I believe also it is the climate control system adjusting itself.

The first time I pulled both the console and especially the instrument cluster I was scared of breakage. The cluster project required me to keep revisiting it with my homemade hooks many times over several months. Finally, I got brave and put additional pressure on. It gave and no breakage.
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'87 300TD - 132K - Soon 4-Sale
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Old 10-22-2004, 12:45 PM
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Join Date: May 2002
Location: Charlottesville, VA
Posts: 548
D_ryan: Hope you had a good visit though- guess where I work...

I'll be in W-burg in the next week or so, there is another guy in the area who has a TD, too.

My new glow plug relay makes my car feel like new! Starts in about half a crank of the starter, idles smoothly with not a wisp of start-up smoke.

Cheers,

JAS

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