The the stock delay wipers on the W123 have a single fixed interval. Often times I found myself wishing for a variable delay of the type found in many modern cars.

However, I didn't want to drill any holes for a delay control so I just lived with it. In an old thread about retrofitting "tap to pass" (Komfort Blinkers) several folks mentioned the lack of variable delay and proposed some custom solutions but the thread died. Fear not - there is a way!

Just like the Komfort Blinker mod VW provides the answer in the form of the 99 relay. This relay adds a variable delay to the factory stalk without any modifications.

With a 99 relay installed the delay position will work as before with a fixed interval similar in length to the Mercedes factory interval. However, the interval can also be user programmed! Simply turn the switch to delay and turn it off again before the wipe is completed. Once the desired time has passed just turn the switch back to delay and the new interval is set. A delay from a fraction of a second to about 30 seconds can be set.

Once the wipers are turned off (for longer than the programming interval) and on again the standard fixed interval resumes. So you can program it if you like or leave it alone. The great thing about this system is how intuitive is. Turn the wiper switch to delay, turn it off again, wait until you want it to wipe again then turn it back to delay. Most cars have an adjustment ring that takes several cycles to get just right. With this system the delay is determined by direct visual feedback. All other stalk functions remain the same. I've been using it happily on an 85 300D for several months.

The 99 relay is found in many late 90's Jettas. It can be found in other VW cars of that era too but the higher spec Jettas often have them. They are located on a relay panel under the steering column and are clearly marked "99" on top. I went to a local salvage yard and came home with 4 relays and sockets. Some cars have a socket block while others have removable single sockets. Sockets can be found in many VW/Audi cars even those without a 99 relay just take note of the pin configuration needed for the 99. VW uses many similar relays with subtle differences in pin orientation and size. Sockets can be re pinned provided they have the correct basic configuration.

The sockets are necessary because the 99 relay uses spade connector rather than pins. Aside from that it will directly replace the W123 delay relay (impulsgeber) without any mods to the basic wiring of the car. If you can solder, you can make an adapter using the 99 relay socket and pigtail with a salvaged Mercedes 6 pin connector. You don't have to hack the harness and you can always return to the stock configuration.

The delay relay on the W123 is located behind and to the left of the instrument cluster. It's possible to remove the relay and install the adapter by removing just the under dash panel but removing the instrument cluster will make the job easier.

The wiring for the adapter is as follows:

Mercedes Circuit # / VW circuit #

31 / 31
15 / 15
86 / T
J / I
31b / 53S
S / 53M

The circuit numbers are printed on the relays themselves.

This mod should work on several Mercedes models but as yet I've only tested the W123.

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1969 220D 5 Speed (OM616)
1983 240D 4 Speed
1985 300D Auto 376K
1985 300D Auto 275K