I just did this mod on my 85 300D. When you get into a hot car, the first thing you want to do is open the windows. This mod will allow you to do that without having to put the key in the ignition first. If you already shut the engine off and forgot to close the windows, you can close them without fumbling for your keys. I have had this mod in my 83 300D for 3 years now without any problems. YMMV.

Disclaimer: Use this at your own risk. If you have kids, this mod is probably not a good idea.

1. Disconnect battery - terminal.

2. Remove the upper right (fuse c aux fan) and upper left fuse (fuse a power window )

3. Strip a short length of 12 gauge wire and shove the ends in the upper fuse clip holes of fuse c and fuse a as shown.

4. Put fuses back, which will secure and make contacts with the wire. Check that you have made a good connection by tugging on the wire lightly and make sure that it won't come out.

5. Connect battery - terminal and you're done.

Enjoy!

How it works:
Power is taken from the aux fan fuse c upper contact (hot at all times) to supply power to the window switch fuses a and b, bypassing the window relay (which is normally energized by the ignition switch in the start or run position). This mod is quick! (takes me less than 2 minutes).

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Very cool.

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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

wouldn't this energize other ignition circuits as well?

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

If it did, this mod would be worthless and I would not have made it into a DIY.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Doesn't this energize the relays for the windows? Don't they draw power in the "on" state?....hence draining the battery much faster if the car is sitting?

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

No: I suspect that it feeds current to the output side of the relay contacts, not the coil.

Safer to disconnect battery negative terminal.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Don't the windows work with Ign off on the 300D anyway....?

Does on my 1985 280TE/300TD 'diesel-converted' car....

There's two relays behind inst cluster that are responsible for this function....
--Uses the courtesy-light supply from door switch to operate one of those relays, the other is to do with the window main supply....

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http://i190.photobucket.com/albums/z...0TDnoplate.jpg

Alastair AKA H.C.II South Wales, U.K. based member

W123, 1985 300TD Wagon, 256K,
-Most recent M.B. purchase, Cost-a-plenty, Gulps BioDiesel extravagantly, and I love it like an old dog.

W114, 1975 280E Custard Yellow,
-Great above decks needs chassis welding--Really will do it this year....

Some cars have a "convenience relay" that allows the seats to be adjusted with the key off so long as one of the front doors is open. I suppose the same thing could be done with the windows.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

You're right, so there's no chance of shorting battery + terminal to chassis while you're disconnecting it.

I have had this mod in my 83 for 3 years now and it does not drain the battery.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Thank you! Thank you! Thank you! .........

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I could not own any MB without the help from you...fellow forum members.


83 300td 207,XXX

Did you do the mod? Is it working?

For anyone worried about battery drain, before you disconnect the battery terminal and remove the fuses, connect an ammeter in series with the 2 fuses (in place of the white wire). There should be no current there.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Will this work on a 240D ?

I did the same thing to my 116. I just wired it beneath the fuse box.

It's also handy when you leave a window open and it starts raining!

__________________
My occupational hazard bein'
my occupation's just not around...
1980 300SD
1980 300SD

It should work on all W123's. Have not tried on others.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked