Okay so I go out to my 1980 W116 300SD this morning. I put in a new fully charged battery. I turn the key it glows. when the light goes out I try and start it and get nothing. i try and reglow again. it glows i turn the key and get nothing and this time everything on the dash goes dim and the glow timer under the hood on the left had side makes a buzzing noise. The 80amp fuse is not blowed on the unit. i unplug and replug both plugs on the unit. now it doesn't even glow, crank, etc. All the lights on the car work fine. I checked the battery and its fully charged. What the hell is wrong. I'm ready to scream. I need my car and can't afford to get it fixed right now. All the other fuseS are fine as well

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1973 280 - Sold
1980 300SD - Sold
1982 240D - Stolen
1988 300E - Sold
1989 260E - Sold
1989 560SEL
1994 E420 - Sold
1997 E420
2005 CL500

Bad connection at the battery? Why did you put a new battery in it?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I replaced the battery cause the one that was in the car was over 7 years old.

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1973 280 - Sold
1980 300SD - Sold
1982 240D - Stolen
1988 300E - Sold
1989 260E - Sold
1989 560SEL
1994 E420 - Sold
1997 E420
2005 CL500

So there were no issues with the battery prior to replacement apart from its age? I still suspect the battery connections.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Yes, checkthe battery connections. If they're not clean and tight, sometimes the glow etc. will work but when you try to start, the high current draw kills the connection (and that will in turn cause low voltage to the relay, hence buzzing).

Take the terminals off, clean them well, screw them tightly down on the battery posts. If that fails, check the positive cable connection at the starter and negative on the firewall.

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kalpol
79 280SE
82 Fiat Spider 2000
81 Fiat Brava
04 BMW R1150RT
96 Jeep Grand Cherokee

This sounds like a bad battery connection. Get a battery cleaner at any auto parts place and clean the inside of the battery cables and the outside of the new battery poles.

You can also just scrape them with a knife, but a brush will do a better job. And make sure the battery cables are tight on the battery poles.

Pooka

Twice over the last 50 years or so, I've purchased new batteries that were bad - both in the last 5 years. Did you buy the cheapest one you could find? I've never had problems with Interstate batteries in my 123.

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Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html

Ground strap between the body and the engine!

Also check the connections at the terminal block. It's a chunk of brass and plastic to which the heavy cables are run and then connected together with nuts on captive bolts. One of them on my car was cross threaded and the connections weren't tight - so once in a while I would see exactly what you are observing.

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1984 300TD