Bradster928

Folks,

I usually reserve my posts to something more serious, but I have to share this.

This morning I was arriving at my mechanic's shop to begin to address several issues on my two-week old 1983 928S, with 59K. Anyway, I cut off the car, pulled the key, but then noticed that my car was still running! In disbelief, I put the key back in and tried again. The key worked in that it would start the car (that is grind the starter against a running engine), but it would not shut the car off.

I then asked myself, "What's different?" For the first time I used the defroster today. I decided to turn it off and, what do you know, the car cut off. I tried to start the car with the defroster switch, but to no avail. Darn!

I do not plan to fix this issue, but it is just one example of the weird things you can run into with an old car.

Thanks for listening.

Bradster928

Speedtoys

Ignition switch.

IIRC..replace it.

Manfred

You figured this out a lot quicker than most! It's a known glitch. The defroster relay needs to be replaced (IIRC). There are other threads on this issue; do a search but I'm pretty sure you just need to replace the defroster relay.

Speedtoys

Ah sweet...I thought it was one of the list of ignition switch issues...

Learned!

sweet928

Actually, that's a built in anti theft device. Lol.

jbrob007

It'll also assist you in draining the battery if your not 100+10% sure its OFF...

Manfred

Well, not so fast, IIRC, my memory can be shaky; you might be right. I don't have time to do search right now but hopefully Bradster will before doing anything...

John Speake

I priced one of those relays today at a Porsche Centre £145 plus 20% tax !!

So I am attempting to repair one for a customer. Several blown compoments and burnt tracks but repair should be possible...

Speedtoys

What does it _do_?

It..fires up a high or low current, and high current has a timer, right?


Could this not be a unit that plugs into the socket, but using modern components does the same thing a ton cheaper?

Hans!

SeanR

Find out and fix the issue.

I have a customer who went to push his defroster button and the entire dash went up in flames. It's taken a year for him to get the wiring sorted out to the point I'd work on it.

Bradster928

I bought (ordered) a new defroster relay for just a few bucks. I hope that resolves the issue. Strangest issue I have ever encountered in a car.

Bradster928

928mac

I removed mine and left it out when I found it was the reason for the battery drain.

Ducman82

i think mine does it when the vent is on with fan on? i can't remember..... but that is screwy. when the car is not on lift bars, ill have to remember to play around with that. never gave it much thought.

John Speake

I am still tracing out the circuit. The device has two high power (40A) relays, plus the timer circuit. There seems to be two modes of operation, lower power demist mode with the two elements in the rear screen in series (heater switch pulled out) and a higher power de-icer mode with the the timer (switch pushed in) which connects both elements in the window in parallel.

Common failures appear to be that the unit can drain the battery, especially when used in "pushed in" mode,which I assume is a lower current drain. Then a more serious high power fault mode which the fuse won't protect.

Alan

This is just a rear defroster relay failure - sounds like your ignition switch still works fine.

Certainly worth fixing this if possible (or passing it on to someone who will take a crack at it) , though you got a good replacement deal here. I'm sure a cheaper ralay would be possible today - however a dual relay will still be expensive and the engineering cost to make a replacement is prohibitive. Though we have heard of this many times - its hardy an epidemic and the relays can usually be found used at reasonable prices.

Alan