HEATED REAR WINDOW SWITCH PROBLEM!!

Sandeep · Jul 5, 2007

Hi

As you've probably read from my previous post about this problem the heated rear window switch keeps turning on by it self now and again and doesn't turn off. I have a 1997 boxster 2.5. I've tried a new switch and a new relay with no success. I was told today by my friend who is a mechanic that it could be a bad earth problem as he has had this problem with other cars.

Can anyone tell me where the heated rear window is earthed to. My friend sais that some cars are earthed to the rear boot lid hinges. Does anyone know where the boxster heated rear window is earthed to. If I can find this I will be able to clean up the contacts and hopefully that should solve the problem.

Your advice would be most appreciated.

THX911 · Jul 5, 2007

It might be worth putting a link to your previous thread so you don't have to repeat the details. I take it that you have had no luck with the guys who did the glass softtop conversion 2 months ago? They should really be sorting this out for you...

Mark_Bennett · Jul 5, 2007

Agreed - please can posters keep updates to the original thread. It doesn't help others who may have the same problem in the future if some information is in one thread, and some in another. Perhaps more imprtantly, the original poster may remember "my other thread", but not every one else will have seen it!(including perhaps the very person who knows what the problem is...[

])

Sandeep · Jul 5, 2007

Sorry about that I will remember to keep it to the same thread in the future. I contacted the company who did the roof conversion and they said I can bring it down to them but the only thing is they are about 170 miles away which is a inconvenience to me. I was hoping someone would know where the rear window is earthed to so I can clean it up and get a better contact. I'm sure thats what the problem is.

Paul Fraser · Jul 6, 2007

If you don't get a reply here try Renntech.org

Richard_Hamilton · Jul 6, 2007

The wiring diagrams show the earth for the HRW (brown wire) going to Ground Point 7. Probably under the passenger seat from the looks of it:

GreenThing · Jul 6, 2007

A poor earth is more likely to switch the heated screen off at random, not on. Try tapping the relay.

Sandeep · Jul 19, 2007

Thought I had solved this problem as it has not played up for 2 weeks then today when I opened the roof the heated rear window switch came on. Everytime I come to turn it off just switches back on again. I've wasted money on a new switch and relay from OPC which has not solved the problem. It's driving me mad. It's one of these intermitent faults which happens and can go for weeks at a time before it happens again. I was thinking of taking it to OPC to see if the fault comes up on the diagnostics but I don't want to waste anynore money if nothing shows up on it.
Does anyone know if it would show on the diagnostics, something is shorting it out or tripping the switch.

Any comments appreciated.

Richard_Hamilton · Jul 19, 2007

A diagnostic check wouldn't be any use, as there is no control module - it is all just hard-wired.

Your problem may be elsewhere, of course, as the supply for the HRW is common with the heated door mirrors. If you would like the wiring diagram, drop me an email and I'll attach it to a reply.

Sandeep · Jul 20, 2007

Thanks richard that would be great. Could you email it to my personal email address if you can't attach it on this forum. My email address is

sandeeptakhar@tiscali.co.uk

I haven't tried the earth yet. You did attach a wiring diagram a couple of posts above this one for the HRW. It shows the earth is under the passenger seat. Could a bad earth trip the switch on?

Glyn · Jul 20, 2007

A poor earth will not switch the screen on - not a chance.
For the window to heat it must have a power source, the switch only puts a nomonal supply voltage to the relay - the relay once activated bridges two terminals to allow the full supply of current - the problem can only be with the relay.
If the switch is off - and i note it is a new one then provided that switch does not send power to the relay to "Excite" it then the relay will not activate, with the main switch disconnected then the hrw cannot work (check this - if it still opperates then you have a wiring fault elsewhere which is sending a supply voltage to the relay - check no bare cables are very close at the relay box that could make contact on a rough road (try banging lightly with your fist on the relay pannel - does this activate the hrw)
Next is the relay itself - i note it is a new one so i would discount getting a faulty relay.

When the hrw comes on - on its own accord pull out the relay - it should go off - this will then leave you with solving what is sending a supply voltage to the relay.

Have you had any electrical work done recently - perhaps a new sound system - is there a chance a newly fitted component has a screww that has penetrated an outer sheath of a cable and is intermittently bridging two cables.

Lastly, how do you know the screen is on - it could be simply that the indicator light is illuminating - which is a different fault - have you put a voltmeter to the screen and earth to absolutly confirm a voltage is being supplied?

Sandeep · Jul 24, 2007

Thanks richard for the wiring diagram.

Sandeep · Jul 24, 2007

Thanks Glyn for that info. The problem arises every 3-4 weeks. It goes for weeks without coming on and then just happens one day. If you switch the car off for a while it seems to solve the problem. The only thing I had replaced was the hood in may. I went for a brand new hood with a rear glass screen conversion. But I can't think why this would cause the problem as they would of only had to un clip the wires that connect from the old screen to the new screen.

Glyn · Jul 24, 2007

Sandeep, check there is a voltage to the screen, i assume you think it is on as i guess your indicator light is lit.
disconnect the plug to the rear screen and attach a 12 volt bulb to the two connections, then if a supply voltage is applied the light will illuminate and prove a voltage is being sent - then back track - remove the switch - does the light stay on or go out.
If the light goes out you have a faulty switch, if it stays on you have something else supplying the voltage to the relay.
Take a voltmeter and check the exciter terminal at the relay with an earth - if no signal then the relay is stuck on, if a voltage is present then another circuit other than the switch circuit is supplying the exciter circuit - start removing fuses to establish which circuit is providing the voltage.

Richard_Hamilton · Jul 24, 2007

Glyn

There doesn't appear to be anything else to excite the relay. This is taken from a 2002 diagram, but the connections are the same as the 1997. The relay is labelled 'control unit'. You can see the switch just toggles the relay one way or the other, giving an output to the HRW, and mirror heaters. I agree that it should be a problem with the switch or relay, but Sandeep has changed those.

It could be that the grey/green wire to the indicator light in the switch is shorting to ground somewhere, which would cause the light to come on without the screen actually heating. Your trick of connecting a bulb to the HRW connectors is a good call.

Sandeep · Jul 25, 2007

Thanks and glyn and richard for the advice. I will try connecting the bulb. I have replaced the switch and the relay as richard mentioned. It hasn't happened for a couple of weeks now.

Glyn · Jul 25, 2007

ORIGINAL: Richard Hamilton

Glyn

There doesn't appear to be anything else to excite the relay. This is taken from a 2002 diagram, but the connections are the same as the 1997. The relay is labelled 'control unit'. You can see the switch just toggles the relay one way or the other, giving an output to the HRW, and mirror heaters. I agree that it should be a problem with the switch or relay, but Sandeep has changed those.

It could be that the grey/green wire to the indicator light in the switch is shorting to ground somewhere, which would cause the light to come on without the screen actually heating. Your trick of connecting a bulb to the HRW connectors is a good call.

Richard i agree with your comments "There shouldnt be anything else to excite the circuit, but if the hrw activates something is sending the voltage and only the circuit from the relay could do this, unless - as my first post, something has been done to the car, and i am thinking of a metal screw that has punctured a series of cables, in particular a live wire and the exciter circuit wire from the switch to the relay-then as the car shakes on a rough road the screw bridges the two cables-sends a signal to the exciter circuit and activates the relay.

I do suspect though that it is simply the indicator light comming on as Sandeep does not say how he knows the hrw is actually on.
we have no frost at this time so nothing will give the game away like the screen clearing.
Dont know where Sandeep lives but i would love to get my hands on this one

Glyn

Sandeep · Jul 26, 2007

Glyn

I live in Northampton, would love for someone to sort this out. The problem is it doesn't always happen. It's one of those hidden faults that come alive every couple of weeks or longer, there is no set pattern.I did notice that when the switch was activitating itself you could here a click sound coming from the right hand side of the dashboard near the relay/fuse panel everytime the switch came on, almost like there was power going to the hrw. Very strange.

Sandeep · Jul 27, 2007

Also I switched on the hrw to see if I could hear that click sound and it did not happen. So the click sound only happens when the hrw switches it self on. I'm wandering if there is something going on near the relay/fuse panel.

Glyn · Jul 27, 2007

Sandeep, my thoughts entirely.
Do the bulb test to prove voltage is being sent to the hrw, when (if) the light illuminates leave it on and remove the switch, if the light goes off on removing the switch you will know it is the switch sending the exciter circuit - replace the switch.
If the light does not go off then go to the relay box - start removing one fuse at a time (but dont pull the htw fuse) one of the other live circuits must be sending the voltage and by identifying which circuit will make tracking the problem a little easier.
If every fuse fails to estinguish the light then pull the hrw fuse, if that extinguishes the light it is a faulty relay.

Dont understand why it is so intermittent though, does the hrw light come on when driving on a particular road - one that is very rough - i am trying to figure out how severe the body flexing has to be before it connects the circuit.
kepp a log.

If all else fails then we can meet up, we are not too far apart and together we will sort this out.