I am having trouble with the sunroof in my '82 300SD. I have unplugged the motor from the harness and checked it with my multi-meter and am only getting 6 volts at the plug. I have tested the switch, verified that I have 12 volts to the switch, and cleaned the fuse holder and replaced the fuse. I have also verified that the motor is good by jumping it to a battery, the sunroof then opened and closed just fine. I also tested the voltage at the plug with the motor plugged in and show 0 volts when the switch is pressed.

What am I missing? Is there a relay in the system somewhere?

Thanks

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

A short or a bad connection? Have you tried measuring the voltage when the plug is under load? Is there by chance a ice cube relay in control here? Replacing those things solved all my electrical problems in my sd

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1981 300SD 512k OM603

I had some of the same issues on my 85 300CD, I ended up removing the switches, roof motor,windows,anntena,and rebuilt them all. Once you pop the switches out, the switch cover pops off at the pivit point of the switch, just be careful there are small springs and ball bearings in there. The old grease from the factory gets nasty and so do the contacts. Clean the grease out with contact cleaner or some alcohal based cleaner and clean the contacts with some scotch brite or what have you. After I did this things got better.

There is no voltage across the plug when it is under load. I tested the switch for continuity and showed 0 K ohms, but maybe it has enough internal resistance to cause the problems. That motor must draw a lot of current judging by the size if the wires that come out of the switch! I'll pick up a new switch at the yard this weekend. The picture on the switch is worn off anyway.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Bump

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

No ideas?

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

OK, I'm bumping this again now that it's starting to get nice around here. I have verified that it is not the switch by swapping in a known working switch. The problem seems to be between the switch and the motor.

Any help would be appreciated.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

There has to be a relay.I wish we all new what ones are for what.Maybe need technical wiring manual.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

this is from a w123 manual, but it's probably the same
http://mb.thatchermathias.com/sunroof.pdf

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg

Check resistance from switch to motor. Mine buggered out this winter too, I assume burnt motor from never cleaning the tube.

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http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

Assuming the setup is like the w123. Then there is no relay between the switch and sun roof. It would be the switch. Although you stated you have good 12 volt power at the switch and the switch is a known to be good, it could be still the switch. They sometimes get full of grease and dirt and act finicky. I would remove the switch and see if you can get the motor to run by jumping the switch's power and ground leads to the two leads to the motor. If it opens and closes as you swap lead connection, then it is your switch. If not then try using another ground source and do the test again. Hopefully is one of those issues.

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1983 123.133 California
- GreaseCar Veg System

The wiring seems to be the same as the W123. I have tried swapping the switch with a known working one from another car and jumpering the plug. I need to find a better ohm meter, mine only works in Kohms which is not sensitive enough for something like this. I wonder if the ground from the switch could be bad...

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Yeah, I would check your grounds.

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-Randy Wakefield

1969 220D 4 speed (parts car)
1976 280C
1976 280S
1981 240D 4 speed (parts car)
1982 300D
1983 300TD (Ivory)
1983 300TD (gold)
1985 300TD (gray)
1987 190D 2.5
1970 280SEL (sold)
1977 240D 4 speed (sold)
1974 280 (rusted to death)
---
1927 Chevy 4 door sedan
1938 Chevy 2 door sedan
1950 Willys Jeepster
1955 Studebaker President 4 door
1977 Ford F250
1979 Glastron 17'
1948 John Deere A
1960 John Deere 2010
1979 Satoh S650G
--
2000 Bichon (Doby)

corrison, bad grounds, loose connections?

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

would it be very difficult to use an electricians "fish tape" to run a new wire from the switch back to the motor?

Once I get all the engine issues sorted out and swap out the springs and shocks - this summer I'd like to get the roof working in mine too....

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95 E300 Diesel 265k and counting