The Germans beat me to it!

W123-Database - Programmierbarer Intervallschalter für den Scheibenwischer

This tutorial has some great pictures of an alternate approach for getting the 99 in a W123. Unlike my mod no adapter harness is required. This is the W123 equivalent of Rick76's mod for the W124.

Google translate will give readable text but even without translation the pictures make the procedure very clear.

I opened some W123 relays and some 99's and found enough unit to unit construction differences to make this approach more of a general guide than a step by step. Even so the end result is plug and play.

I wonder if these could be made to work for a w123?

Programmable Intermittent Wiper Relay | GoWesty

That looks like a 99 relay for a bit more than I paid for 3 on *bay.

x2. Walks and quacks like a 99 relay.

Sixto
83 300SD
98 E320 wagon

I picked up another 99 yesterday at the wrecker. $5.

Beware of eBay sellers with multiple relays for sale at low prices, sellers that have a low of number ratings. I did a BIN of 4 relays from a seller that had 7 for sale. Listing said located in Spain but shipping showed from China. The seller modified the ad to double the price after I bought mine so I figure they discovered that they sold them too cheaply. Three weeks later and they haven't been shipped and the PayPal payment has yet to be accepted. No response to emails so I figure they are trying to avoid honouring the sale.

Edit: Beware of eBay seller pavlblokhi_0 and simkhachatrya_0 (same person) if they relist these relays.

Mine came right away from Latvia.

Know when to hold them, know when to fold them. I hooked up a 99 relay using wires with spades on one end and tail light connector pins on the other as a test. No joy. I had a friend far smarter than myself properly solder the 99 relay board to a MB wiper relay pin set. That did it! The first time I set it for a 10 count it stayed at the OE 5 count. Then I tried a 2 count and it worked. I tried a 10 count again and it worked. It's worked since. I guess it thinks it's in a CANBUS system that's has to get acquainted. The downside is I lost the double wipe mist feature when tapping the washer switch. It's probably better this way.

Sixto
83 300SD - has variable delay wipers which the 210 doesn't!
98 E320 wagon

I noticed this at first as well but then discovered that the washer switch had to be triggered for a couple of seconds before you get the extra wipes.

Right you are! IIRC any tap if the washer switch gave at least three wipes. Now a quick tap gives a wipe and a full press gives at least three wipes. What's not to live?

Sixto
83 300SD
98 E320 wagon

I know this is an older post, but does the VW 99 relay go in PLACE of the Mercedes relay, or is it in addition to the Mercedes relay where both are in the car?

In place of

Sixto

Hey Sixto, can you explain in detail how this hooks up? I read the above but need clarification.

Disqo, do you have pictures or information about the wiper relay that you got from techguy512? Perhaps we could make more if we knew how he did it