I have a 71 220D, I did the upgrade to pencil style plugs, and a relay about 8-9 months ago. But now, with new batteries and all, I can't keep a charge. I put a battery in and it will start right up and run. If I don't undo the battery at night it drains entirely.. no power.. I have not found anything on ... but remember reading about the glow plug relays in the past.. is this a good place to start?

Can you put an ammeter in series with the disconnected negative lead and the battery to see how much current is being drawn from the battery? It's possible that something in the new relay is wired wrong and is "on" all the time.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .343,000 miles Wife's car
2005 E320 CDI . . 148,000 miles My car
Santa Rosa population 177,300 (2026 projected)
Total. . . . . . . . . . . . 668,300
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

pull each fuse 1 by 1 while the car is off and test for a draw using a multimeter. If the terminal has power when the key is off and it shouldn't then you have a draw on that item(s).

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

If your relay was installed 8-9 months ago, I would not jump to guesses.
I had this happen with a bad voltage regulator.
With the car off, key off. Will the alt. pull a wrench to it like a magnet?
If so it is the VR. If not I would go to the fuse box as suggested.

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83 300SD Dark Silver Dark brown inside

Before tearing things apart and replacing things. What are your voltage measurements at the battery?
......with the car off (if it's the glow plug relay or something else drawing it down, you should be able to see it on a meter)
......with the car running......both DC and AC volts (at start-up and after a short charge time)

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Sam

84 300SD 350K+ miles ( Blue Belle )

Thanks for the help