Your readings are not unusual. These motors run on current through an inductive motor. The voltage will "appear" to drop to zero as the only resistance is the windings. The only true way to determine a problem is with an amp meter connected in series.

Both power and ground are switched...... through the switch itself. This is how the motor changes directions.

Most of the window switch problems I've had are dirty contacts (probably due to their location). Pulling and soaking in a cleaner, such as electrical contact cleaner, then drying them thoroughly has always resolved the problem.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Only one terminal is switched (from power to ground) per switch actuation. The remaining terminal is not switched unless the switch is actuated in the opposite direction. (In which case the originally switched terminal isn't.)

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

It's hard to explain. At rest, both sides of the motor are powered. Direction selects which side is removed from power and ground is applied to.


OOPs! please note reason for editing!

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Sam

84 300SD 350K+ miles ( Blue Belle )

Evidently, my schematic-reading abilities are not what I thought they were. Same for a volt meter.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

No, you're reading fine.

Both terminals are powered 12V+ at rest. The motor doesn't run because potential is the same at both leads. When you press a button, one side or the other is switched to ground. Ground is supplied through the brown wire on the driver's switch, not locally in the door.

You don't need to measure current: since your motor works when powered directly, not a short circuit.

If you have power at both leads at rest, and you're sure there is no power on both leads when you press a button, the only explanation that makes sense is a bad switch. What you may want to do is measure RESISTANCE between each of these terminals and ground when you press a button. That would determine is whether they are simply disconnected, or switched to ground.

The left and right switches are NOT interchangeable, that's not a test. You need to buy or borrow a good left side switch and try with that.

It is for the W123133 (as noted on schematic) This covers several years up to 1985.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

How about the driver side rear? It is on the same circuit as the Passenger front.

This link may be of some help, although I don't think it provides the answer you are looking for.

Mercedes power window repair - Finninday

It does look like it is most likely the switch that is the problem.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

The only "133" that I see is the page number.

In any case, I have the 1982 Electrical Troubleshooting Manual; it's not the the same as your schematic. My terminal numbers might not be correct for an '84.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

OK, this was where I was heading...I was stuck on the fact that the drivers side switch - when installed on the passenger side - also did NOT operate the motor. But, if the switches are NOT interchangeable, then that could explain my problem (and I was wondering about the interchangeability due to the middle button connection on the driver's side switch that locks out the rear windows).

ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

That's why I recommended that you jumper the connector terminals. But the terminal numbers that I provided might not be right for an '84. The basic idea can be garnished from the provided schematic, even if the terminal numbers and wire colors are different.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

I admit is not clear just what that 133 means. I see in the later ETM that the power windows schematics are on pages 132 and 133, so you could be right.

Regardless, it seems I do have the later schematic too. If the switches have internal LED backlighting, then this schematic should be correct (it is for my 85)

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

It's the page number. No doubt about it.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

I admitted that you could be right, but you just don't give up do you?

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

OK, so does that make your terminal numbers correct - to test my ground?

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE

Set your meter to Resistance. Then with switch plug disconnected, connect meter leads between pin socket 4 on the switch plug and a good ground. If I recall correctly, there is a ground connection driver side near shift lever (but any chassis ground will do). If the ground is good, meter will read 0.00. If it is not connected to ground, it will read Infinite (very high) resistance.

You might try applying 12v from external source to pin sockets 1 and 2 and see if motor runs. If it does and ground was good, then get a new switch.

If it does not run, another check would be to disconnect green and black wires inside door. Then measure resistance from pin socket 1 to green wire inside door and from pin socket 2 to black wire inside door. They should read 0.00 if the wires are not broken between door and switch plug.

Good luck with it.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5