W 124 rear wiper

[Mercedes 190E]

Guys
The rear washer hasnt worked on my 300 TE since I got it, although the wiper works fine in all modes. Finally got round to having a look....
Stripped out the washer bottle, blew the pipework through and took the motor off to test on a battery. The motor seemed shot so I substituted a new one (Tested and working.) However, still no washer. Measured the volts through the pump wiring and when the switch is held in, it fluctuates between 10.5 and 0.3 volts, in time with the sweep of the rear wiper. Obviously though there isnt enough power to work the motor.
Does anyone have any ideas where I should look next? Would it be a relay or switch or a wiring fault?
(I am a bit handicapped in my fault finding by not having a wiring diagram!)
Many thanks.

 

[television]

If this pump is built into the rear panel door, then a broken wire on the hinge area would be the place to look.. What I do to get readings without damaging the cables is to push a pin through the plastic into the copper and measure from the pin.

Again the dash switch could also be faulty

 

[Mercedes 190E]

Thanks Malcolm. The pump and reservoir are under the boot floor rather than in the tailgate though, so I'm not sure how that could affect the wiring. I dont suppose you know of a wiring diagram for the W124 anywhere? It would REALLY help in tracing the wiring back.

 

[television]

Sorry john I cant do 124 diagrams, or any diagrams as the component on the diagram cannot be printed.

I forget where the switch is now,,but if its on the stalk, then this can be cleaned successfully and accounts for most of these faults.

Forget any wires if as you say its in the body and not the tail gate

 

[Mercedes 190E]

Just found a wiring diagram of my system ! (On T'interweb,....) here:
http://tinyurl.com/9as77b
All I need assistance with now is interpreting it! Most seems straightforward, but what does the yellow/blue wire from the wiper motor to the switch do? It seems to have an impact on the washer connections-have I got that right?
Thanks.

 

[television]

The Yel/BE is the live feed, taken from the wiper motor

 

[Mercedes 190E]

Aah ! So a break in that wire could be the problem? If so, I could check it at both motor and switch ends to be sure...but I do have a fluctuating voltage at the pump so maybe its more likely to be the switch ?
Thanks for your help Malcolm.

 

[television]

Sadly broken wires and switches can look the same on a meter.

I think that it is wired the way it is so that the washers cannot be operated without the wipers,,think that I am right there.

One snag with a voltmeter is that it imposes almost no load on the circuit under test, what I do here is to wire a small bulb across the meter contacts, there by loading the circuit under test

 

[Bolide]

I believe the feed to the pump passes via contacts on the wiper motor so the pump only operates at specific times. So there will be a live feed (or an earth) from the switch going into the tailgate via the wiper motor and out again to the pump

You can find out whether it's a switched live or earth by checking the connections on the pump

have you tried putting 12 V across the pump to see if it pumps OK?

Nick Froome
www.w124.co.uk

 

[Mercedes 190E]

Hi Nick
Yes, the pump works fine when connected directly to a battery and I think it is the live that is switched. What I DONT understand is the fluctuating voltage seen at the pump when activating the switch, as in my first post. That would seem to indicate that the wire from motor to switch is OK, but not enough voltage is reaching the pump to drive it.
I wish I understood car electrics.....

 

[television]

Car wiring is a little bit different in that every wire that can be saved helps on the cost and weight of the car, so unusual wiring techniques are employed to avoid having cable runs running parallel in the same circuit

 

[Mercedes 190E]

Thing is, I don't even need the rear washers really, but if a car is intended to have a feature, then I feel strongly that it should work. Unfortunately, I cannot afford an auto electrician at present and so need to solve it myself. I must confess that of all the cars I have owned, and forums I have belonged to, I am not sure why Mercedes electrics are such a black art. The wiring diagrams for my 124 are much less complex than my old Rover 827 yet they seemed to be more logical somehow. I think I'm just getting old....
Anyhow, any further advice on how to test this circuit to narrow down the problem is greatly appreciated, and I am grateful for the help so far!!

 

[roofless]

Hi Nick
Yes, the pump works fine when connected directly to a battery and I think it is the live that is switched. What I DONT understand is the fluctuating voltage seen at the pump when activating the switch, as in my first post. That would seem to indicate that the wire from motor to switch is OK, but not enough voltage is reaching the pump to drive it.
I wish I understood car electrics.....

i would guess it's a poor connection i would trace it back from the pump to the switch ect.i had the same thing with my horn on my 124 it had some voltage then none every time i tested it would differ but in the end it was a poor solder.2hrs to find & 2 mins to fix

 

[Bolide]

If the pump works and you get volts via the contacts on the wiper motor it sounds like either the contacts are u/s or there's a cable break or oxidised connection

I'd strip out the tailgate trim, locate the plug for the wiper motor, trace the feed to the the pump and test it by applying 12v. If it works OK, check the incoming voltage with the washer switch on. If that's OK, try jumpering past the contacts on the wiper motor - that'll tell you if the contacts are at fault

Nick Froome
www.w124.co.uk

 

[television]

If the pump works and you get volts via the contacts on the wiper motor it sounds like either the contacts are u/s or there's a cable break or oxidised connection

I'd strip out the tailgate trim, locate the plug for the wiper motor, trace the feed to the the pump and test it by applying 12v. If it works OK, check the incoming voltage with the washer switch on. If that's OK, try jumpering past the contacts on the wiper motor - that'll tell you if the contacts are at fault

Nick Froome
www.w124.co.uk

It is best to take off existing wires before you run wires as many components do not like a reverse flow through them. and great care is needed re the plus and minus feeds

 

[Mercedes 190E]

Thanks very much guys-plenty of food for thought there. I will strip the tailgate down at the W/E (I have to change the courtesy switch anyway) and have a fiddle with it. My thought is that maybe the power is not getting from wiper motor to pump, but we shall see! If I solve it, I will of course report back.....

 

[television]

Thanks very much guys-plenty of food for thought there. I will strip the tailgate down at the W/E (I have to change the courtesy switch anyway) and have a fiddle with it. My thought is that maybe the power is not getting from wiper motor to pump, but we shall see! If I solve it, I will of course report back.....

The last person to clean the switch built into the rear lock had 100% success.

I do have a paper on that switch.

In simple terms for the washer, take off the live lead and run a lave 12v wire to it and it should run if its OK,,this being the case it will be a fault between the wiper motor and the washer, not forgetting that the switch may need cleaning.

When you get it apart I can talk you through it,,I will even phone you

 

[The Crooner]

John

When you have it all working can you pull the hose from the resevoir by the fuel tank, to the jets, and tell me where you think mine might be broken?

I took the tailgate trim off and took out the locking mech - awesome piece of engineering. I corrected the rear interior lights not going off, but now they only go on from the rear doors not the tailgate. Malcolm's work instructions and drawings are useful.

Will have to take it all out , sure I have something not connected quite right.

Think I have totally fixed the idle problem - taking the car to Leicester tomorrow, and I'll report back then.

Tony

 

[Mercedes 190E]

Malcolm
Many thanks for the offer-that paper might well be useful if you could send it to me ? (Going to strip it all down this weekend.)

Tony
Sounds like you had the same prob as me-my rear courtesys wont go off (Had to take the bulbs out.) My understanding of the problem is that my tailgate microswitch is jammed on. That would mean that although your switch is no longer jammed, it now isnt making contact at all. Did you clean it, and if so how?

 

[The Crooner]

John

You'll see when you get the lock mech out that it isnt easy to identify what is what.

I just sprayed Servisol at anything which looked like a switch, but it was cold, over Christmas, and early one morning. As soon as we get a warm day I'm going to do it all again.

You will need to ensure that all of the hard links to the mech are broken - they pop out, and that all of the cable connections are undone.

And you will scrape the skin off your hands and wrists in doing so.

Best of luck

Tony