Diagnosing wipers not working on W124

[Mike S]

Hi,

Having procrastinated about stripping down and re-greasing the wiper mechanism on my 1990 300TD Estate, due to the fact that it had the early, screwed on aluminium rather than plastic clip on wiper mechanism cover (and not having read the suggestion to drill a hole in the bottom of the unit in which to spray grease!), my wipers have now stopped working altogether.

I am now trying to determine the cause. Unfortunately, it is not a blown fuse.

I have read that there is a plug that can be disconnected so that one can supply power directly to the wiper motor to test its operation. Can anyone please tell me where this is located and which pins to use?

Can you also please tell me if I should be able to hear the motor running, in the case of the gears being stripped and the wiper not moving?

I also understand that there is a thermal cut out for the wiper motor. Can you please tell me where this is located and whether they are ever known to develop a fault?

I can hear a relay click once, when I turn the wiper stalk control to the 1st and 2nd positions but not when I turn it to the 3rd. I suspect that I may have bad contacts in the switch, as playing around with the switch in the past has usually got the wipers to work (slowly) in the 1st and 2nd positions. Can you please tell me what I should hear and confirm which relay controls the wiper motor on the W124?

Any other suggestions would be appreciated.

For anyone else who has a similar problem, the following threads might be useful:

How to lubricate the wiper mechanism: http://forums.mercedesclub.org.uk/showthread.php?t=26200

Front screen wiper not working:
http://forums.mercedesclub.org.uk/showthread.php?t=34388&page=2

Complete windscreen wiper diagnostics & repair instructions:
http://mbworld.org/forums/c-class-w...-wiper-diagnostics-repair-instructions-2.html

N10 Relay, Soldering Repair, Wiper - Indicators & Hazards - Rear Window Demister.
http://forums.mercedesclub.org.uk/showthread.php?t=62702

Wiper has started working on it's own
http://forums.mercedesclub.org.uk/showthread.php?t=38617

I should like to take this opportunity to thank 'Dec' in particular for his very helpful posts.

 

[television]

This is the circuit of the wipers

http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1995/E320/SYSTEM WIRING DIAGRAMS/5460.pdf

We seldom have problems with the thermal trip, but anything can happen, I have seen one where these contacts were bent and could not close.

With a voltmeter you could put it over the plug contacts to see if you have 12 volt, that will save a lot of searching

 

[Mike S]

Thanks for your immediate reply and the circuit diagram. Very helpful.

I have just got the wiper assembly out (which wasn't as difficult as I had feared - apart from one rusted screw) and am about to see if the motor is still working.

FYI, the only connector on the motor lead appears to be the plug on the motor itself, which is inaccessible unless one removes the whole wiper assembly from the car. With hindsight, I think that I might have tried applying power direct to the stalk contacts to see if the motor worked before I embarked on stripping down the whole wiper assembly.

 

[television]

I would take care in applying power to the stalk, they are so easily damaged. I cannot remember if the 124 has a bonnet open switch that stops the wiper from running when the bonnet is up, there does look to be one on the diagram

 

[genbryan38]

I have 1993 w124 convervitble, when turning the wiper switch on, not only does the wiper not operate, but the windows and seats quite working for a while. Not sure where to start, has anyone had this issue?

 

[brianbrian]

I would take old fuse out even if it looks o.k. And replace it. Then clean relay contacts. Hope this helps