Perpetual Porsche Electrical Idiopathy

On a delicious sunny day I was driving along, minding my own business, when all of a sudden the windshield wipers turned themselves on to maximum speed, thereby smearing the windshield's bug collection all over the place. No frenzied, animated manipulation of the windshield wiper switch would shut them off, although the speed did vary somewhat now and then, but they kept on going. I had to come to a halt at the side of the road, shut off the car, open the trunk, and pull out the fuse for the wiper circuit so that I could drive home in peace. Grrr.

What's that missing wire? The functions of all the others are obvious.

The first thing I did was to begin some research online, and I found many references to similar problems, with an equal number of references to suspicious windshield wiper switches as being the probable culprits. Getting the switch out was a straightforward operation once the steering wheel was off, along with sundry other bits of the steering column, and when I removed it a piece fell out from the middle of the switch. Aha!

A small bit had broken off (plastic . . .) from the portion of the wiper switch mechanism that controlled the windshield washer function. That little piece coaxed the switch to stop squirting when you released the lever, which you pull toward you to pump washer fluid onto the windshield and its bugs. Why should this have anything to do with the wipers turning themselves on? Well, it was broken and not all there anymore, so I figured I had to replace the switch in any case, whether or not this had an influence on the wipers turning themselves on, so I went back online to order a new one.

My car is a '74. Evidently, the switches for the 1974 and '75 cars differed in some way from all other such switches, whether before, or after those years. A switch for the '74 model is NLA. Things that are no-longer-available immediately skyrocket in price if anyone has a new-old-stock example in their possession, because even an odd part like this has a market for it somewhere in the world. But, the prices didn't go up, because there simply weren't any to be had, so there was nothing to raise the price on. Grrr, again.

Of course there are used switches to be found from the Porsche recyclers, but why would I want another 40 year old plastic switch that was likely to self-destruct several minutes after I installed it? One guy I sometimes communicate with, who lives a few hours away as the Porsche flies, has been rebuilding old Porsches for 25 years, and he told me that he has more than twenty old switches like this on hand, but he was too busy to sort through all of them to see if any of their part numbers matched mine. Hmm, it would take a full day to drive there and back, what with chatting and all, only to find, possibly, that he had no matching switch, and all of them were ~40 years old, so I didn't take that drive. 

The new switch is the fatter one with a picture, not text.

I admit, this is a First World type of problem; a perfectly matching wiper switch for my Porsche was challenging to find. Boohoo. Nevertheless, you need wipers if you want to drive and it starts to rain, because you don't want to be blinded by the sprinkling and have this cause you to bump into an incautious moose at the roadside, rudely plopping him into the mud. Naturally I contacted another (once upon a time) Porsche restorer, but he lives just around the corner, only 15 minutes away. He said he had a solution. Get a new switch, he said, one for a newer car, and he could make it work.

He knows plenty of stuff about old Porsches, but he won't tell you all of it, because what he knows equals his bread and butter, so I had to discover the following on my own:  The difference between a 1974 switch and a 1976+ switch is the fact that there is a different picture on the end of the stalk, and the stalk is made of plastic (!) instead of metal. Otherwise, the wiring is identical. I further discovered that my turn signal switch/arm had already been replaced at an earlier date, and it matched the design and material of the new wiper switch that I bought. Serendipity. I now have two matching switch stalks. Is that all there is to the difference between the NLA '74-'75 switch stalk and a newer one? In a word, yes. That, and they threw in an extra brown ground wire with the new switch, one that has female spade connectors on the ends of it, because the later switches have intermittent wiper function for which this is required, whereas the intermittent function was optional with the earlier models.

One of a number of ground clusters on my car.

Porsche went crazy with the wiring on these earlier cars as we see at the top of this post, and they especially liked redundant grounds in many circuits. I don't know where that disused brown ground wire mentioned above went, but I could have connected it to just about anything and the car probably would run better simply as a point of correct Porsche protocol. For example, Porsche calls for a ground wire to be attached to part of the bracket that holds these switches in place, and the wire then is to attach to the dashboard which is an integral part of the car. What? That bracket is bolted or welded to the dashboard of the car, so why does it also need a little skinny brown ground wire connecting the two? Seems kind of anal retentive. Bad grounds can be blamed for a variety of electrical ills, but there must have been a simpler way.

In another feat of engineering brilliance, Porsche built these midyear cars with the relay controlling the wiper motor positioned inside of the dashboard, instead of adjacent to the block of fuses in the trunk. You can't get at those relays if they fail, unless you remove all the heating and ventilation ducts and controls from the trunk, along with the air plenum, and other bits. Never mind that simple business, on my car the relay is built into the wiper motor itself, so it's necessary to remove the instruments, reach your arms through the resultant holes in the dash, and fiddle with the relay blindly, no tools allowed. You can't get the relay out this way, you can just fiddle with it, but that's what it took to get my wipers working again (courtesy of my Porsche guy), not the replacement of the switch, so I didn't need to buy it in the first place, but now it matches the turn signal lever at least. How long the relay will continue to work is anybody's guess, and it will be necessary to take half of the car apart when it fails again and sends my wipers into a frenzy.

The wiper motor as seen through the speedo hole.

Odd electrical gremlins are routine with these cars. Many discussions on the Porsche online forums focus on electrical circuit peculiarities, and in my experience some reasons for this are a lack of fuses to protect some inaccessible circuits (fire!), plain old rotting wire insulation in a car of this age, connector corrosion, as well as maddeningly complex attachments that could be simpler than they are.

To be continued if I figure out what the missing wire is in the picture at the top. I'll need to consume extra protein to do it.