R129 Wipers/Turn Signal Control Unit

[greybowman]

Any help or advice on the following gratefully recieved.

On a recent trip, my wipers (which are not used very often) were initially very slow before stopping completely after only about 1 minute. I also noticed on returning home that (a) the heated seats were not working, and (b) the turn signals would signal a LH turn whether the indicator stalk was moved up or down.

After reading a few posts on this (and other) sites, I decided to take a look at the control relay - top LH in the attached picture with white writing (Part No 140 820 71 26). I tried to unplug it in the same manner as the adjacent relays unplug, but it would only lift around 4cm before it was clear that something (felt like wires attached) was preventing it coming out. After the attempted removal though, the seats and RH Turn Signals were once again working correctly. When the wipers were switched on however, the motion was again very very slow (didn't even make one sweep), and I could hear and feel a rapid clicking coming from the Control Unit. I had previously thought that the wiper motor could have failed, but with at least some movement there I guess not.

My queries are:

(i) is this a wiper motor problem or could the problem be the control unit itself?

(ii) how do I remove the control unit? I am reluctant to pull too hard and risk damaging wires.

(iii) have I located the correct control unit? Does this control heated seats, indicators and wiper motor?

For reference, the car is R129 SL320 1998 (V6 1999 model) and has 51,000 miles from new.

Many thanks.

 

[Dec]

In the absence of a better reply, there are a lot of leaves in the vicinity of that box, perhaps the area has gotten wet/damp and that is the cause of the fault.

I have never gotten any deeper than you have on my W202 but there is one screw at the bottom of your picture, which if removed may allow you to hinge the fuse tray upwards, it must come off somehow.

If you can get in there check and clean all the connections, putting the wipers on to the intermittent wiper setting will allow you to feel and hear the relay click every 5 or 6 seconds if you put your hand on the relay unit.

You have located the correct control unit all right, the indicators and wiper motor are a common fault associated with the control unit, the heated seats, I don’t know about.
Its unlikely to be the motor as the indicators are also faulty.

Dec

 

[greybowman]

Thanks for the quick reply - good point about the screw at the bottom of the tray.

The leaves by the way are several years old, the car has been garaged and only run on dry sunny days for the last two years - hence the wipers not used very often.

I can feel a very rapid clicking from the Ctrl Unit - about 4 or 5 times per second as the wipers struggle to move.

Thanks again.

 

[stats007]

It's the combination relay - which does fail.

 

[recycled]

all relays pull out, Not sure on yours but it may be the green or black one in front of it.
Just try carefully.. No wires attached to it, it would have pins that fit into a socket much like a plug for your radio / TV.
What you can do is write the numbers on all the relays and google them.
It should tell you which relay number does what. be careful as the ABS relay is there as well.

 

[greybowman]

Thanks Recycled - yes, I have removed the relays already. It's not the relays, its the large control unit to the LH of the relays and it definately doesnt have pins as it will lift about 4cm before it seems that it doesnt want to come any further.

 

[recycled]

does your demister get affected as well?
try this post 6

http://www.benzworld.org/forums/r129-sl-class/1320980-turn-signal-rear-window-defroster-wiper.html

 

[Dec]

What about the battery, is this its first outing this year? Check that the battery is fully charged and remove each fuse to check that the are in good condition.

Try assisting the wiper motor, by giving the wiper arm a push (not excessive force and mind your fingers) when it is switched on to intermittent and normal speed. If this gets it going then it might be the motor, if not, then probably the relay controller.

Dec

 

[recycled]

its not the motor. I have the problem as well. it is that relay. Called N10 in the 202 and expensive as well.

 

[Dec]

its not the motor. I have the problem as well. it is that relay. Called N10 in the 202 and expensive as well.

On a W202 its number 2, just pulls out you say, thanks didn’t know that.

Dec

 

[stats007]

Thanks Recycled - yes, I have removed the relays already. It's not the relays, its the large control unit to the LH of the relays and it definately doesnt have pins as it will lift about 4cm before it seems that it doesnt want to come any further.

N10 is the the combination relay module - or control unit as you refer. The clicking is the internal relays not latching.

 

[Ardveen1]

1996 r129 sl320

Hi,
I am having the same issue with slow and intermittant wipers. I also tried to remove the Relay 140 820 71 26 and it is loose in its location in the relay compartment of the fusebox, it pulls up easily with slight resistance. The resistance I think is also the wire loom being lifted with the upward motion. The gutter below the windscreen fouls a clear lift upwards, I wonder if this is removed are the attached wires and connector block below long enough to allow a disconnection from above if sufficient clearance is available on the uplift ?

 

[Dec]

Have you lubricated the wiper mechanism, if its not lubricated it can also cause the wiper to slow or stop in mid sweep, see… https://www.youtube.com/watch?v=1gCCl_xZhB8

Got a picture of the area in question?

Dec

 

[Ardveen1]

Mercedes Sl320 R129 1996 N10/2 Relay

I removed the relay last night, with the help of my phone light app. Here is the steps I used to remove the relays

Open bonnet to vertical, tabs on hinges on left and right.

Remove the mesh trim below the windscreen, 3 x philips

Remove the plastic gutter below it, 2 x philips, pull the fixing tab forward to clear the metal lip and then work the tab under the metal to allow the complete item push back and release itself from the centre casing sorrounding the wiper mechanism,

Remove the fuse cover, clips off

Remove the fuse cover housing below this, 4 x philips

Remove the single philips on the front centre of the fuse / relay carrier tray.

Lift the tray with the with the front tab and pull forward. There is a moulding / recess in the casing to the rear which the tray slides into, pulling the tray forward releases it from this recess.

The fuse / relay tray can be lifted up a bit, carefully, to view the bottom of the N10/2 relay ( 140 820 71 26 )

There are various separate connector wiring blocks on the bottom of the relay, I pulled them all out quite easily, starting from the front , a 6 pin etc until I got to the larger block on the rear of relay.

This relay has a sliding locking tab, there is a bit more freedom now on the relay as the other wire blocks are free. slide a small screwdriver behind the sliding tab on the rear side of the relay, it will pull back, the movement is visible on the side as the locating pin slide rail is visible, pull the tab back all the way, the push the plastic housing and the unit will pull out.

Be careful as the wiring block came loose in my case from the plastic moulding but fortunately all the wires / pins are held in a plastic grid and they remained therein, I just have to examine this sliding rail / wiring block in daylight to understand exactly how it works.

Anyway, removed the relay closed up the fuseblock, and bought a replacement relay on ebay.

The forums do talk about cleaning the N10/2 relay, it look to me that this particular unit cannot be opened, the PCB appears to be inserted from above and the cover ( with the writing ) glued down. I prised off this cover, but this is a far as I got, I think I will damage the casing if I try to force the board out. I will spray some contact cleaner into it and give it a gentle air clean with a compressor.

I will try this at the weekend while waiting for delivery of the new ( used ) replacement part, you never know it just might work.

By the way, it was wiper intermittent and slow that stopped working completely, fast was ok, as was hazard lights.

I think that possibly there might be enough slack on the wiring block connectors to leave the relay / fuse tray in place and still allow the wiring blocks to be connected to the N/10 relay before dropping into position in the carrier tray. I will know at the weekend when I try the re-installation.

I will install in reverse order, starting with the large block with the sliding lock tab and moving to the front of the relay. ie in the direction towards the standard fuse carrier blocks.

Hopefully this might help someone else, alot on the forums on this issue, but not much on this particular combination relay, 1996 models and probably later ones.

 

[Dec]

That’s a lot of work to get to a component like that.

Both types of N10 relay xxx 821 00 47 and 140 820 71 26 do open quite easy as seen below.
It’s very likely to be a broken solder joint on the PCB that’s at fault, if you haven’t already, see here… N10 Relay, Soldering Repair, Wiper - Indicators & Hazards - Rear Window Demister. - Mercedes-Benz Owners' Forums

Dec

 

[Ardveen1]

N10/2 Relay - R129 SL320 - 1996 model

Hi,

Interesting view of these relays. Alot of electronics contained within.

Further to last email, please disregard the bit about pulling back the tab with a screwdriver. The wiring connector block that receives the pins from the relay is housed within a sliding rail, this rail extends to about 2/3 the length of the relay casing, you simply push the inner end of the sliding rail towards car windscreen direction, this motion has the effect of lifting the wiring pin block up and it unlatches the complete assembly ( wiring connector block + sliding rail ) from the bottom of the relay. DO NOT remove the wiring block connector from the sliding rail mechanism by removing the rear small wrap around locking mechanism that fixes the pins into the connector block. I mistakenly did so and it is a pain to get them back in again. They are housed within a plastic grid so at least the wires did not get mixed up. Patience and inserting a small nail into each pocket until they all line up and pressed into the block and back on with the 3 sided wrap around locking rail and a bit of levering to prise it over the 4 small pins. Warning - no need for this so do not remove it.

My relay is the same as the bottom picture. The larger combination relay,I managed to get the top off but my numerous attemps at releasing the pcb base plate failed. An experienced member from another forum kindly offered to open it and check the solder so hopefully it may be repairable. ( €530 from MB Ireland to replace )

I did buy a replacement from Ebay before the repair offer arrived. I have fitted that but the very same issue arises. Fast wipers work fine. Slow and intermittant do not although they tried very slowly and moved a few inches and stopped. I can hear something click when I turn on wipers to first setting but still no movement in slow / intermittant. Could it be that the relay I purchased has the same issue. The seller sold it on the basis that it was working.

So now there is a few possibilities, maybe the relay is still the issue. Is there any way of testing the combination with a multimeter?. Could it be something else?. as the fast wiper works 100% I assume there is no issue with the wiper mechanism itself.

A bit disappointing thast the replacement did not work but hopefully I will get some good news from the generous repair offer. I would love to know if these is a test to evaluate these relays. There was one posted for the OVP on a W124 which helped my to get my E220 CE started.

 

[Dec]

The fast speed, 3, and slow speed, 2, have nothing to do with the relay, I’m almost certain about that, on that basis it may be that the old and new relay are ok and it is the stalk switch that’s at fault.
If it is the stalk switch that’s at fault, then it will need to be replaced, you can try cleaning it with switch cleaner but I don’t think anyone has ever had any success with that but worth a try anyway.

There is a test that you can do as in link below.
Post #16 here… Wiper issue - Page 2 - Mercedes-Benz Owners' Forums
Also post #2… Wiper has started working on it's own - Mercedes-Benz Owners' Forums

Did you lubricate the wiper mechanism as in video below, very important that that is done?
See… https://www.youtube.com/watch?v=1gCCl_xZhB8

Dec

[YOUTUBE]1gCCl_xZhB8[/YOUTUBE]

 

[Ardveen1]

R129 SL 320 Mercedes 1996 model

Hi Dec,

Thanks for the reply.

This sets me on a new route which is worth investigating.

I dismissed the stalk possibility but now that the relay is changed with no result then the stalk is my next target.

Intermittant does not work and neither does slow but fast speed is fine with wipers stopping wherever on windscreen when fast turned to slow / off etc, ie not returning to base unless switch off timed to coincide.

I will run this test on the stalk and later advise.

Thanks again

 

[Dec]

I had a problem with the N10 years ago, car 1994 W202, I removed it from the car, I was then able to run the wiper on fast speed 3 and slow speed 2 but if wiper switch was turned to intermittent speed 1 then the wiper blade wound stop dead on the screen at the moment the switch was turned to 1 or 0.

In your case, if slow won’t work when in speed 2 position then its likely to be the stalk switch that’s at fault.

In my case, it was a broken solder joint on the relay PCB that was at fault and not the stalk switch. The N10 relays job is to kick off the wiper motor in intermittent speed 1, time it to sweep the screen at 5 second intervals and also bring the wiper blade back to the park position when the wiper is turned… in mid-sweep… to off 0 positions.

In your case, if the stalk switch is at fault, then removing the relay won’t prove anything.

Dec

 

[Ardveen1]

R129 SL 320 Mercedes 1996 model

Hi

Thanks for the reply.

I pulled off the tip of the wiper stalk and pushed the lower sleeve down to expose the inner shaft.

The SL is different to the photo, the is no obvious green wire, the is however a slot below the two plastic tabs which locate the outer casing when it slides up. This slot looks like it is a locking tab for the inner mechanism. i wonder if the lever to change wiper speed is set at 0 and power sent to the visible switch posts at 1, 2 would that tell the same thing ?.