Porsche 928 Electrics

Electrical information & supplies for late model 928s

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Front Intermittent Wipers:

I think the analog faster/slower control for the 928’s factory intermittent wipers has several major problems: Mine had an insufficient range of speeds (~ 4 sec – 18 sec interval), it is always difficult to set quickly to the right frequency for any specific conditions and the control is ergonomically challenged – its an awkward location to reach & also confusing (which way for faster?). This whole issue repeats since the rate you need constantly varies.

This didn’t seem in keeping with the ergonomics of the rest of the major controls - even the other front wiper/washer controls that are in my opinion well though out, effective & quite intuitive. I wanted something better!

Looking for a Digital Option

I like things to be digital where it makes sense - but only where it makes sense (e.g. for me this means definitely NOT for volume controls). However intermittent wipers seem to be a “made for digital” application, since the variable here is time and we can digitally define a required time instantaneously.

After some checking of the wipers (manual, wiring diagram, actual operation) I determined the following standard operating modes prior to the changes:

Wiper Stalk Functions – Normal Operation:

# Wiper Stalk Action


#0  Off Position       

(neutral horizontal position)

#1  Pull Backward stage1

Washer Jets while pulled +3 wipes after release

#2 Pull Backward stage 2

Washer Jets & fast wipe - while pulled then +3 wipes

#3  Push Forward    

Headlight Washer Jets (only if headlights up)

#4  Push-Up  (Tip Switch)

One Wipe on slow speed (or more if held in place)

#5  Up 1 Click        

Wipers on slow speed continuous

#6  Up 2 Clicks       

Wipers on medium speed continuous

#7  Up 3 Clicks       

Wipers on fast speed continuous

#8  Down 1 Click    

Wipers on Intermittent (interval via rotary control)

Rotary Rate Control

Intermittent interval set (~ 4sec – ~20 sec)

#1-#4 are momentary (tip) switch actions, #5-#8 are locking switch actions

I thought a digital version relying purely on the column stalks would be a big improvement. Get into intermittent mode and use the stalks to indicate when you next need the wipers to wipe and have that automatically become the new intermittent wipe frequency. Wow sounds easy right...  and actually for once it is…

Turns out other manufacturers have faced the same issue and have come up with control module/relay solutions for this. Fortuitously VW has a very similar relay that meets the standard wiring & footprint of the rather expensive and “flawed” Porsche intermittent relay (here Porsche/VW collaboration has real benefits for us!). Although the VW relay has 1 fewer pin this only affects the connection to the rate control potentiometer which is no longer needed anyway. So it’s a direct plug in replacement and works perfectly! My thanks go to David Hendrickson for being the first to prove out this idea by doing a relay swap on his vehicle.

With the replacement relay here’s my new intermittent operation (all else remains unchanged & isn’t dependent on the relay)

Wiper Stalk Updated Operation:

#8 Down 1 Click

Wipes once & intermittent* (interval defaults ~6 sec)

*Intermittent behavior is the only change

Switching to intermittent mode the wiper will wipe once and start an approx 6 second default repeat cycle (this is improved vs. whatever random cycle delay was previously set on the potentiometer for the factory system).

If after switching on you switch back to the off position & then back to the intermittent position when you desire the next wipe the wiper relay sets the new intermittent rate at the actual gap between the last 2 wipes. To change it again switch to off and back to intermittent at the new rate you’d like (longer or shorter) the rate can be set anywhere between continuous wipe & approx 30 seconds delay. The rate defaults back to 6 seconds between uses (off-time >30 seconds). The rotary control is no longer used for any control function in the new operation – it becomes quite obsolete.

Comparison of Porsche & VW Wiper Relays:










It works great! It’s easy to use and has an intuitive operating mode – even without any knowledge of the systems operation you have the default 6 second intermittent function. It requires no modifications to the wiper wiring and the Porsche factory module can be swapped back in at any time.


It took more time to remove the carpet & access the relay panel than to do the actual relay swap. The only possible hard part is actually removing the old relay – fortunately the tall can on the original Porsche part allows an easier grip than most of the other relays. 

Part number you need VW part # 3B0 955 531.  Make sure you get the programmable delay type - sometime the part numbers do change... but there is a similarly numbered part that only has a fixed 6 second intermittent/delay wipe mode (beware!)


Copyright (c): Alan Moore 2006, 2007, 2008, 2009       Page Updated: 04/03/2009