W115 Intermittent Wiper Relay Needed
 

I have a 1974 240D and the intermittent wiper relay went bad (also known as the pulse sending unit).

JeffreyNMemphis helped me find a new part on the internet and my local dealer said that they had to go to Germany for the part.

Peach Parts will have to order the part.

Does anyone on the BB have an extra part and would like to sell it. I'm in Oregon and it's raining out here. I can wait for the special orders, but the wipers will be going too fast for the 3 weeks or so - not that big of a deal but I thought I would ask if anyone had one for sale.

The part number is A115 821 00 63. I have pictures if you want me to shoot them off to you.

Thanks,

Dave

I will take a look in my stash of relays and let you know if I find one , is it a large black relay or small silver ?

I have one from a MY76 in front of me. They made a change from the earlier ones like your's by eliminating one relay. The one I have is p/n A 123 821 00 63. It won't work in the earlier years, however looking at the solder connections on the relay as well as the connections coming from the pins, they look to be possible problem areas. As well there are 2 electrolytic capacitors that are also suspect (47uF 16 volt).
You could check the relay coils and contacts with an ohmmeter. Coils should read just under 100 ohms.
The one I have here also has the component leads cut off very short so they could have cracks in the solder joints.

Have you opened the relay up to give it a visual inspection? Might just need some re-soldering.

Hi Guys,

Attached are pictures of my relay.

I'll look at the solder joints and check the ohms on the coils. The contacts have a bit of pitting and the relay pivots have a bit of play in them. I don't know enough of what is good and what is bad.

I'll also check the solder. I don't see any cracked joints, but I'll reflow a few suspect places and see how it works. All of the caps look good. It would be great if I could get the unit to work.

Getting these old electronics is a pain.

Thanks for the suggestions and the help.

Dave

Images of Pulse Sending Unit
 

Here are the images of the pulse sending unit.

no luck here sorry. :o One more box to check but doubtful

I measured the resistance across the coils - they were 91 and 93 ohms. I also tried to measure the resistance across the contacts and they were very low. I just used my Harbor Freight DVM so I couldn't push any current across the contacts or the coils.

I'm afraid to file the contacts. They are pitted (not polished smooth) but I don't know how bad is bad. The caps aren't leaking and I don't have a method to test them either.

Does anyone know if TechGuy512 is still rebuilding these so one can program the delay time? I tried to find his website and couldn't find it.

Dave

Thanks for looking Meltedpanda!

Dave

You said in your original post that the "wipers will be going too fast for 3 weeks or so". Are you saying that you don't have low speed as well as no intermittent wipe?

Your circuit board looks slightly different than my '76 besides having 2 relays. Don't file the contacts. You could use a narrow strip of 600 or finer sand paper doubled over to run though the contacts. Clean the contacts after by running a piece of paper through (could be soaked with alcohol). Slight looseness of the contact pivots is normal.

If doing any soldering you must add some fresh electronic grade solder. Reflowing alone is not adequate.

Your relay coil resistances look good.

I went searching and found another box of modules. I did find one with 2 relays but there is no Mercedes part number stamped on it. It does have the same number that is moulded in the case as yours, however the other one that I have (single relay) also has that number. The relay would have come from a '74 280 that I scapped years ago.

I will test it before I say too much. I will change those 42 year old capacitors before shipping it to you. I see what you mean about the relay pitting. Mine is quite bad as well but I will replace the relay with the one in the other module that I have as it is like new.
Shipping would be from Canada if you can't get yours fixed and want this one.

Hi Rick76,

I"ll try to sand down the contacts a little on my relay and see if I can make it work. There is a couple of used units on eBay(which are probably like mine) or I can special order the unit from Peach Parts for $150 or so.

Thanks for looking and your advice!

Dave

I sanded the relays and reflowed some of the solder. It still isn't working. I don't think I will tackel to replace the caps. :-(

I'll look into getting a new unit.

Dave

There are new old stock ones on EBay now for $65. 4 available.
Item number: 252279732064

Hi Rick76,

Thanks. I contacted the guy and he seems legit. I hate to buy NOS from a guy on EBay, but the local dealer wants near $200.

I think it would be best to get a new one.

Thanks for the lead!

Dave

Dave,

Even a new one from Mercedes is likely to be NOS as they probably haven't produced those modules for a few decades.

If you pump the floor pedal for windshield washer fluid, do you get a timed wipe?

Had you checked your stalk switch with an ohmmeter (low resistance scale or continuity) by the way? You can also check the switch intermittent wipe contacts by testing to see if you have 12 volts on pin 1 of the module (probably the easiest way). Also check to see if you have a good ground on pin 5.