W124 rear washer pump

[3ps]

My W124 estate rear washer pump has never worked but I decided to fix it.

I took the connector off and my wife pressed all the right buttons (on the dashboard) and the connector (not I) was turned on and off at the appropriate times.

I took the pump out and hooked it up the the front washer system and it worked!

So if it works and there is power in the connectors.... then why won't it work?

When testing the rear connectors I used a multimeter on the metal cylinders and not on the wires. the cylinders are spotless.

What gives?

 

[television]

The rear wash pump is wired via the wiper, and takes its power from there, often the wires can break around the hinge area. I have the wiring diagrams somewhere

 

[3ps]

Thanks.

But if there is power at the connector that goes into the pump attached to the washer bottle? As I hit the switch on the dashboard I can see the power at the connector going on/off.

 

[television]

You can only check for 12 volt by putting the meter leads on both terminal on the pump, not one lead of the meter going to ground (body)

 

[Ellsy Tanners]

You can only check for 12 volt by putting the meter leads on both terminal on the pump, not one lead of the meter going to ground (body)

If thats the case then a problem on the ground wire, as malcolm says a problem in the connector between tailgate and car is quite common..

 

[3ps]

I took my multimeter and put one pin on one connector terminal and one pin on the other and set it to 20V. As my wife push the button on the dash the screen read 12V on and off. As far as i'm concerned this means the power is getting to the connector.
The pump also works at the front of the car but when I put the rear connector on it it doesn't. I cannnot understand this.

I have a limited understanding but if this still means that the earth to the tailgate is damaged then I will check it out.

 

[television]

Though I have some 14 test meters inodd cases I use a test lamp, just any bulb12 bulb with two wires soldered on, and connect across the suspect item, you can see the bulb light working single handed.

If there really is 12 volt present, the the pump has an intermittent connection inside and it was just sods law that it worked when you moved it.

There is not any more to it

 

[Number_Cruncher]

Yes, as Malcolm hints - sometimes, using a high resistance multimeter can give misleading results.

If there's a bad connection anywhere, while the circuit is delivering virtually no current into the multimeter, there's no voltage being dropped across the bad connection, and so, the multimeter reads correctly.

As soon as you try to draw some current, by using a more realistic load, like a decently sized test lamp, and current begins to flow, the voltage drop across the bad connection becomes significant, and the voltage across the test lamp is not sufficient to light the bulb - or to spin the motor in your case.

You have a bad connection or contact somewhere, and in the wiring between the car and the tailgate which flexes every time you open the tailgate would be where I might look first.

 

[Ellsy Tanners]

Yeah use a test light and see if it lights, chances are the earth is poor, do a continuity check of the earth pin tip body may have a high resistance.

 

[3ps]

I guess I could just put a wire from the earth connection ot the body and press the button to see if it works. There is a convenient earth screw near the rear light cluster I could use.

 

[3ps]

OK so I took apart the connector going into the rear pump. It had two wires with those cylinder connections.

I got a seperate wire and hooked up the earth pole on the pump to another earth on the chassis and it didn't work. I tried all combinations of wires and poles and nothing worked.

But when I put the pump into the front washer it works.

Surely what I did should have been enough?

 

[Mercedes 190E]

I can sympathise ! I have EXACTLY the same problem with the pump in my TE and have tried everything you have. In addition, it was suggested to me that the live wire from the motor to the switch/pump might be at fault, so I disconnected the motor and fed 12V directly down the feed wire. That didnt work either!

 

[W124-300TE-1989]

I can sympathise ! I have EXACTLY the same problem with the pump in my TE

Ditto!
Would love to know if either of you ever solve this!
MW

 

[television]

I will try and print out the info for you

 

[Alex Crow]

guys, the problem is in the wiper motor. there are copper contactors that make a circuit on a metal plate on the nylon drive gear. gunge, corrosion and arcing have ruined the current carrying capacity but it will still tickle your mulitimeter. strip down and you may be able to repair, but i doubt it.