w140 wiper trouble - PeachParts Mercedes-Benz Forum

locry · #1 12-01-2012, 10:14 PM

95 S280

My wiper only functions with speed setting "2". Doesn't respond with positions 1,3.

I opened up the wiper relay... I don't think the relay contacts are the problem... aside from being "clean"... only one relay "clicks" which leads me to believe that the problem lies BEFORE the relay. (technically 2 relays work, the green one clicks as soon as I turn the key)

I have dismantled the combination switch, isolated the 4 wires/pins at the stalk that control the wiper. 3 colored wires, which I'm assuming are for the 3 speed settings... and a black wire that shares itself with a bigger black wire which I assume is ground.

Connecting each of the colored wires to the black wire only one gets continuity, in speed setting #2... coincidentally, on setting #2...testing continuity across all 3 colored pins yields continuity. Does this mean my combi switch is toast?

To make matters more confusing... I decided to bypass the combi switch and "short" the wires on the corresponding connector... same result!!!!! The wiper motor turns only when connecting the pins which respond to speed setting #2!!! (black wire and one of the colored wires)...

What controls the intermitent and full speed settings? Just the wiper relay? As far as I can tell it looks brand new inside... and if it were the contacts... the relays should at least "click"... but not all of them do.

Any theories? Is there another "brain/module" that controls the wiper speeds?

Pili380SL · #2 12-02-2012, 08:58 AM

I believe the combination relay (N10) controls the speeds and the K26 wiper relay only controls power/no power.

locry · #3 12-02-2012, 10:05 AM

Thanks... it seems that way. I opened up the combination relay and nothing seemed amiss as far as the relay contacts are concerned... but there are a bunch of ICs and stuff that I have no clue how to check.
However... the combination relay has 3 connectors, the middle one it seems, has a mini plug/connector that goes into the connector. It goes into one pin. I dug around the fuse box and found a single plug that MAY be the one that goes into that single pin. Will try that out tomorrow. The middle plug I'm referring to is also a single large diameter pin type deal... the missing single plug is smaller in diameter. I hope that's it.

oldsinner111 · #4 12-02-2012, 10:15 AM

was the car flooded over wiper motor?

locry · #5 12-02-2012, 10:18 AM

Wow... I just read this...
Anybody know how to test W140 Combination Relay?
I never knew controlling wipers were complicated!!! That's hi-tech for you all. It's not as simple as on/off anymore... resistance and minor variations of whatever... I can't stand it!

locry · #6 12-02-2012, 11:11 AM

Quote:

Originally Posted by oldsinner111

was the car flooded over wiper motor?

Yes it was flooded, the first time it was submerged 2 storeys deep, second time was just a storey deep.

... But good news!!! That single pin plug that I mentioned... I dug it up again and connected it... VOILA!!! Wipers work!!! And the flasher, and the signal lights too... (I thought it was a different circuit...to be tackled later)

Tomorrow I'll "re-arrange" the wiring inside the fuse box... it seems I jumbled up the four main looms that go out the fusebox grommets. Pulling that smallish plug in the process.

locry · #7 12-03-2012, 07:53 PM

I finally got it to work... at first I thought it was because i connected that smallish plug. Then I thought about it some more... that smallish plug's wire was quite a stretch from where it was positioned in the fuse box... surely Merc engineers wouldn't have designed it that way... then I realized I also cleaned the back of the PCB for some minor oxidation. SO I went down... disconnected the small plug... and it still works!!! It wasn't the plug after all... it was oxidation which bridged a few circuits.
Having the wiper work resulted in a few other things working too... like the turn signals and flasher.