Porsche 928 Electrics

Electrical information & supplies for late model 928s

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Rear Wiper Improvements:

After fixing the flaws in the Front Intermittent Wiper Controls I decided the rear wipers needed improvements too...

My biggest initial complaints are with the switch location for the rear wiper. Its co-located with the sunroof & windows - which to me makes no functional sense. The switch is also positioned so the activation position for the rear wiper is next to the "open" end of the sunroof and passenger window switch (what?) So If you make a mistake is selecting the correct switch to activate the rear wiper - you end up opening a window or the sunroof - eh...? how does this make sense.

Porsche is renowned for its thorough well though out engineering and excellent ergonomics so who the heck came up with this abomination? (I call them the infamous "B-team" of engineering dummies).

I also don't think much of the switch-gear design: 3 wipes for every press of the button... why?

I have modified my rear wipers to be controlled by a push and rotary switch on the main pod - located right where the original rear wiper switch was located in the 1978 model (and using the original stock knob but with a stock rear demister switch body).

New rear wiper switch location








New rear wiper switch - stock on a 1978 I have
mated it to a rear defroster switch body though





When I press the knob briefly (<0.3sec) I get a single wipe, when I press the knob for longer (>0.3sec) I get 3 wipes like the stock mode. If I turn the knob to the active position I get a wipe every 6 seconds  or if I switch off and back on I can set an intermittent digital delay mode just like with the front wiper intermittent mode.

Just for fun I added a mode that initiates 3 rear wipes whenever reverse gear is selected if the front wipers are on (in any mode).

This required swapping the rear wiper delay relay for a standard relay plus adding the same VW digital wiper relay I used for the front intermittent wipers and an additional regular relay for the auto-wipe function with some simple electronics to distinguish between the short and long button presses. 

Overall I like all the new features - especially the new location of the knob - where the rear demist switch used to be - that was moved where the hazard switch was - which was moved to where the Dash Reset Switch was which is itself relocated to the under pod switch location (the std. location for ROW cars) & also to a console switch (the std. location for 1989 cars).

When I added the rear windshield washers I also included an automatic rear 3 wipe mode triggered every time the washer jet button is pressed & then released - a standard practice for all front washer modes and an extra input on the wiper relay provides this feature directly.


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