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Discussion Starter · #1 ·
Hello,

I have recently brought my car and only had to use the rear demister the other day, the switch lights up to say its on BUT nothing happens window stays steamed up. Any help with this would be great......

Thanks
 

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Platinum BFuk Member
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If im right, there are two connectors on the rear screen normally (can someone confirm;) ), one will be an earth and one will be a 12v supply, make sure you have a good earth and also check you have 12v with a voltmeter or circuit tester, both can be bought from a good motor factors.

Also check each individual heating element strip on the rear screen and make sure none are broken.

Im new to bmw's aswell but these are the checks i would usally do, oh and also check the fuse!!!

Hope this helps, let me know if you need an explanation on how to check the earth and power(12v).
 

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Discussion Starter · #3 ·
If im right, there are two connectors on the rear screen normally (can someone confirm;) ), one will be an earth and one will be a 12v supply, make sure you have a good earth and also check you have 12v with a voltmeter or circuit tester, both can be bought from a good motor factors.

Also check each individual heating element strip on the rear screen and make sure none are broken.

Im new to bmw's aswell but these are the checks i would usally do, oh and also check the fuse!!!

Hope this helps, let me know if you need an explanation on how to check the earth and power(12v).
Help on how to do this would be great
 

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Platinum BFuk Member
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Like i said, there should be two connectors on the rear screen usually one on each side about half way down ( they may be hidden behind some trim) and they should be a single flat spade connector, buy a multimeter from a motor factors, nothing special, should set you back a tenner or so.

On the multi meter select 12v DC setting, there will be two probes supplied with the meter, put the black one to a body ground (i usally use a bolt going into the body of the car) and the red probe to one of the connectors(with the demister switch on) check if you have 12v reading on the screen of the meter,(really you could do with a wiring diagram to determine which connector 12v should be supplied to, sure there is one on this site!).

Think this is okay, if anybody wishes to add to it please feel free.
 

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Platinum BFuk Member
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Oh and for the earth, select continuity on the meter, put one probe on body ground, and one on the connector, the meter should beep at you indicating that the wire you are testing is ok and not damaged i.e broken. Or select the 10 ohms resistance on the meter, put the probes as mentioned in the other test, the reading for a good earth should be less than 1ohm, but satisfactory in my opinion is anything under 2ohms.
 

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If there is voltage at the connectors as mentioned above, then unplug both connectors and you can measure the resistance of the heating element as a whole. Open circuit reading will mean a break somewhere in the element.
 

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Discussion Starter · #10 ·
I have now cleaned the connection & check the wiring all is ok, checked the fuse and did not look that good so replaced it so now waiting for a wet or frozen morning to check it out will post if ok or not

Thanks for all your help
 

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Rear Window demister. BMW 325tds year 1997

Hi Folks,
Back window demister not working for some time.
when you turn on switch it lights up the switch as normal. But does not demist.
Took it apart this evening expecting 1 cable on one side and a second cable on the other side of the rear view window. However much more complex. 2 cables on each side connected to the window, --- but on 1 side (drivers rear) there is a white box with a wire (brown i think) going into it and the other wire coming out connected to the window. What is this white box??

On the other side (passanger side rear) i have what i think is an antenna box with approx 4 wires on one side and 2 coming out the other side connected to the window. Are these connections and boxes standard?? Which wires are the ones actually powering the rear window. Why is the power going through these boxes first??

What power do the strips take. Can i connect a switch through the battery and put + and - each side of the strip. ??

Any help would be greatly appreciated.

Thanks
 
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