sanjay28

I'm having a strange problem with my rear defroster on an 88 S4 Auto. While driving the car this evening, I turned on the rear defroster by pushing the **** on the pod. The light (headlights were on) became brighter indicating that it was on. I tried to turn it off by pushing the **** again, but it would not go off - I assumed it would turn off automatically like in newer cars.

I got home and parked the car, not giving it another thought. About 1 hour later, I went into the garage and noticed that the rear defroster was still on. The car was off, but the defroster was still on (the **** was still lit). I do have a problem with my interior lights not going off (I ordered new pins and will fix that next week). Are these systems related or do I have something weird going on? Thanks in advance for your help

Mrmerlin

pull out the defroster relay . They can sometimes stick so open it ans smell it for burns and clean the contacts . If its burned then you may have a bad ground or dirty relay pins
BTW the defroster switch has 2 on positions one is to push for the timed shut off then the twist CW is on till turned off

sanjay28

Thanks MrMerlin. I did notice a buring smell shortly after I turned it on, but I assumed it was from outside since the window was open and the smell went away pretty quickly. I went out to check again and it did go off, but it must have been on for at least 4 hours after i turned the car off. I'll pull the relay in the morning and clean the contacts. I will probably go ahead and remove and clean all of the relays while I'm down there since I have not done that yet since I got the car.

You said that it may be a bad ground - how would l check that? Is the a ground wire from the switch on the pod or is it connected to the realy?

StratfordShark

It does sound almost certainly like a sticky relay. I fixed same problem with new defrost relay.

A workround is to shut off ignition, then restart car. This should force relay to drop out.

Mrmerlin

there is a bundle of ground wires on top of the CE panel when you get there you will see them a bunch of brown wires bolted to the chassis. get a fuse relay chart here print one off www.928gt.com its on page 2 under tips and links

Landseer

There was some talk here two or three weeks ago about the switch sticking in the pod, also.

And, some discusson about that condition back-feeding through to the ignition and keeping the car running in some cases with key off. Weird.

Tails

The defrost switch can be dis-assembled and repaired, if required.
Tails 1990 928S4Auto

sanjay28

Thanks all. I did not get a chance to clean the relay today (3 young kids and a wife that works on Saturdays). I should get around to that tomorrow. If that does not take care of it, I'll try to repair the switch.

Mrmerlin

I would not repair the switch until I had replaced the relay.
Figure it this way, the switch is a hi quality part and its not used much so the chances are quite good the switch is fine

Nightfly

After pressing the switch in to engage the defrost as opposed to defog, do you have to press it in again to turn it off? I swear that when I bought the car, the switch stayed pressed in after doing so, but now just pops back out to regular position even after turning it to the defrost setting. Or...once pressing it in is it in defrost mode for a time, then automatically switching back to defog on it's own?

WallyP

The push-in switch is a momentary contact switch that energizes a timed relay. The only way to turn it off before it times out (assuming that it is working correctly) is to shut down the ignition. If the relay is sticking (unfortunately, all too common), you will have to shut down and restart the engine to get it to release.

Bertrand Daoust

I think this is a VERY COMMON PROBLEM!.

Does anybody as open the relay and clean the contact to se if it solves the problem?
I did that with mine but never tried it again so I don't know if it actualy works.

encyclia

Just got my 85 (black/brown) a couple of weeks back. Was driving with the wife and we were checking the electrics and I turned on the rear window defroster. The **** lit up. I pressed it again and it stayed on (tried this with switch in both 0 and 1 positions). I figured it would go out on it's own and forgot about it.

Three days later, I go to start the car and the battery was low and wouldn't turn over the starter. I suspected the rear window defroster. I checked the original user's manual and it specifically mentions that you should make sure you turn the defroster off to avoid battery issues.

However, the manual appears to indicate that it should turn off if the button is pressed again (in the 0 position at least), so I may have a faulty switch/relay too?

JG928S4

my fuse is baked, never looked into it, but suspect....

JayPoorJay

Crazy switch!!!

A timer you say?