Yesterday, my 300D cranked very slowly at the grocery store. I headed over to Jiffy Lube and had them put their tester on, suspecting a bad battery.

They told me the battery is fine, and is getting charged OK. Sure enough, when I cranked it afterwards, it cranked just fine.

It was fine earlier today, but on the way home tonight, the lights were getting very dim at idle. I pulled it into the garage and shut it down. I noticed that when I turned the key off, the inside light got brighter. Then, I turned on the headlights, and they were nice and bright. When I turn the key to the on position, though, everything gets dim. Turn it back off, and everything is bright again.

The alternator light has not come on at all, not even dimly. When I had a bad voltage regulator, it would glow.

I would think it might be a shorting glow plug, but I wouldn't think they'd be on after driving for 20-30 minutes.

Any ideas of things to check?

Just a wild guess but I would check the E fan on the radiator to see if its locked up and "dead heading" the electrical system.

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Satan creates nothing: he only ruins everything. He does not invent: he tampers. And his followers are no different ~ Archbishop Carlo Maria Vigaṇ

Hmmm...well, I checked it, but it turns freely.

Let me add some more info: the lights are still bright in the "Accessory" position; only "on" is draining power.

Try pulling fuses with the key on one at a time to help isolate which circuit is pulling the load.

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Satan creates nothing: he only ruins everything. He does not invent: he tampers. And his followers are no different ~ Archbishop Carlo Maria Vigaṇ

Thanks...yeah...I was kinda thinking maybe I ought to do that to narrow it down.

I'm just a bit exhausted from cutting up a big tree that fell in the storm last night, blocking my driveway...back out to the garage.

Make sure your glow plug relay is not sticking in the closed position.

I had that happen once. I replaced a voltage regulator and an alternator before I fugured out what the culprit was. Doh!

My symptoms were similar to what you describe.

__________________
Joe

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1980 300SD - 495k miles - 'The Ambassador'
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Former Family Members
95 C280
73 280SEL
90 300D
87 300SDL (X2)
86 560SEL
84 300D
80 300SD

You are Da Man. That was it! Now, I need to track down one of these relays.

Tune up your chain saw and get rid of all those trees so they won't interfere with MB work again !! Steve

After I discovered my problem I had to plug and unplug the relay for every cold start.

I did it this way for a few months until I was able to locate a good used relay.

I don't think the glow relay for he 123 is nearly as expensive as the 116. I didn't see one in the store here but Phil can probably locate one for you if you'd like new.

__________________
Joe

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1980 300SD - 495k miles - 'The Ambassador'
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Former Family Members
95 C280
73 280SEL
90 300D
87 300SDL (X2)
86 560SEL
84 300D
80 300SD

Electrical problems like you discribed are hard to find .... removing one circuit after another is one approach .... in other words, remove a fuse to make that circuit off line .....
Since you had a slow cranking as a first sign of the problem, indicating a poor connection in that electrical system, I would clear all electrical connection from and to the starter motor, ground wire to the frame, both terminals connectors on the battery, both posts etc..and connections on the starting motor .... the only connectors left are inside the starter motor, which at this time assume to be fine and the motor itself ......
As a double check, have the battery check again, Auto Zone does it for Free and checks the current draw from the starter motor which is very important ......

Bill
1981 300 TD

Might want to open the relay and check for cracked solder joints and resolder....fixed mine....

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1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)

Thanks again...I looked around and found a Borg/Arnley for $179 and a "Standard Motor Parts" for $112. Not too bad. Unfortunately, I just had to replace the power steering pump last month.

OK...sounds like an idea worth trying.