Garage => Interiors & Exteriors => Topic started by: DialecticDielectrics on 28 November 2010, 06:54 PM

Title: 2 Electric Windows Suddenly Go Out
Post by: DialecticDielectrics on 28 November 2010, 06:54 PM

My driver-side windows had been working fine, but both of them suddenly went out at once.  I bought a new console switch, and that didn't seem to do it.  After removing the door panels, and hooking the voltmeter up to the leads, I get the proper voltage responses off of the switches. 

Because everything up to the leads seemed to be working, I bought new motors, but when the leads are hooked up to the motor terminals, the motors still won't run. 

Any ideas? 


1976 450SE in Portland, OR
Title: Re: 2 Electric Windows Suddenly Go Out
Post by: koan on 28 November 2010, 07:44 PM
My driver-side windows had been working fine, but both of them suddenly went out at once.

No idea but the wiring diagram for the windows is the library. Look for the "Electric Trouble Shooting" manual for your car  here (

Simple circuit for front windows, rear is only slightly more complex with the extra switch. Note that there will be 12 V on both sides of the motor with the switch in the middle position, activating the switch replaces one of the 12V to the motor with a ground.


Title: Re: 2 Electric Windows Suddenly Go Out
Post by: Japes on 01 December 2010, 12:15 AM
other side is working ok?

Try running a direct wire from the batter to the terminals on the motor and see if the window moves that way.  Gives you some idea that the motors are okay.
Pretty sure fuses are crossed over so shouldn't be that.
Pull the switches out and make sure they are connected properly. If one wire is wrong or has come undone both front and back will go out.
If you're game try shorting the connections at the switch (with the switch connected but the rear plastic cover of the switch removed) and see what happens.
Title: Re: 2 Electric Windows Suddenly Go Out
Post by: DialecticDielectrics on 14 March 2011, 11:36 PM
Alright, I’ve finally gotten around looking into this more.  With spring around the corner, I’m going to need those windows down!

When I hooked up the motors directly to the battery, the old motors worked fine. 

Using the voltmeter, with one probe on a lead and the other probe grounded to the door, I got 12V.  When activating the switch, 12V went to 0V.  With both probes on the leads, the meter read 0V-- which makes sense if they both independently have 12V, right?  However, when I pressed down on the switch, the voltmeter continued to display 0V. 

(Similarly, when I poked the voltmeter probes directly into the wires near the switch, I got 12V, similar to the leads at the end of the wires.)

Seems to me that all the wiring is fine all the way up to the terminals that connect to the window motors.  However, it seems that there must be some malfunction in the switch’s function to replace one of the 12V to ground when activated (see Koan’s note) seeing as how activating the switch did not cause 12V to go to 0V. 

I noticed in the manual that there are 2 types of switches, and that “the 1 terminal has 2 alternate positions” :


Do these 2 positions vary according to the left and right side switches?  The 2 switches I have are identical.  Is it possible that I have 2 right side switches, and that this could explain all of my problems?   (When my windows first went out, I immediately suspected the switches, and ordered a new driver’s side switch, but perhaps it wasn’t actually a driver’s side switch this whole time…).

Could simply getting a proper driver side double switch solve my problems?  If so, where's a good place to order one online?

Title: Re: 2 Electric Windows Suddenly Go Out
Post by: koan on 15 March 2011, 01:57 AM
Just to fill you in on how it's wired...

The two centre console switches are different, one has a push button in the middle and and extra pins on the bottom, the other has a blank black piece in place of the push button.

The button is to disable the switches on the rear doors but still let the driver operate the rear windows. There are three wires running to each rear switch, two of the wires are the +12V pair, one of which goes to ground when the console switch is operated, the third wire is a ground so that the rear switch can put a ground on one side of the motor. The push button disconnects the ground in the disabled position preventing the rear switch activating the motor.

In My RHD car the switch with the push button is on the left (passenger side) which makes no sense for RHD so I assume the switches are in the same position for LHD which would make sense.

Don't know if the console switches can be plugged into the wrong connectors.

Getting the wrong switch would a) be give you an extra push button that did nothing, or b) prevent the rear door switches from operating. Does not affect front windows.

On both console switches pin 1 should connect to ground, pin 2 on one of the switches is switched ground for the rear switches. Pin 1 is in a different position on the two switches, the pins are numbered on the switches.

Here's a really poor quality phone pic of the two switches. Not OEM switches but the cheap replacements which are rubbish, buy M-B ones.

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