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Mercedes W123 Windshield Wiper Relay Repair

Picture of Mercedes W123 Windshield Wiper Relay Repair
How to fix the intermittent setting for the windshield wipers on your Mercedes-Benz W123.  Usually if the intermittent setting stops working, this is due to the windshield wiper relay (P/N 0 335 320 018) "going bad".  This instructable will show you how to remove the relay, test the switching of the relay, and fix what is really failing on this part (the capacitors).

When I purchased my 1985 Mercedes 300D, the windshield wiper intermittent setting (detent 1 on the wiper selection bar) did not work properly.  When selected, the windshield wipers would either work exactly like the slow and continuous setting (detent 2) or they would be intermittent for a cycle or two and then go back to slow and continuous. After some googling, I found out that a relay is responsible for turning the wipers on and holding them off for the short delay and was the source of my problem.

To purchase a new (used) relay on ebay costs approximately $30.  This seemed too much for me and I don't know of any good junkyards around me, so I decided to take the relay out, open it up and attempt to fix it.  After only a little bit of work and some light soldering, I was able to fix the relay and now it works just like new.
 
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Step 1: What You Will Need

What you will need:

No. 2 Phillips Screwdriver

Soldering Iron

Solder

Vacuum Desoldering Tool (Not strictly necessary, but incredibly helpful)

47 uF/16V Electrolytic Capacitor (QTY: 2)
*Note: These can be rated for higher than 16V.  The originals are 16V, but a higher voltage rating (25V, 35V) is fine.  However, these MUST BE 47uF so that the timer delay (RC Timer) in the timer circuit is preserved. These can be purchased at RadioShack.

Flashlight

Something that can give you at least 12V (2 9V batteries, One 12V Battery, 12V Power Supply, etc.)

Brasso

Windex
moonshine885 months ago
I have an '84 300d and they are great cars! if you do an egr delete (easy and free takes a soda can a knife and about 15 mins) the alda delete (free and takes few wrenches and 15-30 mins depending on tools and experience you have) and a rack limiter removal (unless your highly skilled at mechanics and have loads of Patients I'd avoid this several hour headache but its worth it too) these cars will run like champs for ever! I get screamin fuel economy and with the egr and alda gone it gets with it at a stop light now almost fast enough to beat that guy on his rascal scooter across! haha. also straight pipe it they're not really that loud but free air flow helps on a 30 year old plugged exhaust. also the valves need kept adjusted it will make a huge difference all around (12-15k miles/15-20k kilometres) if my intermittent wipers quit I'll pull up this bookmark and try it first but glad someone enjoys the w123s enough to make an instructable on them!
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