Article:

That have been the problem with my car since I've got it 1 month ago, the demister wouldn't work, but I didn't have time to look at it until last nights, when I just got my car back from garage, I list out what I've done to attack this problem.. (All the notes that I have given is what I've worked out last night, some information could be wrong, but read and see if it helps.. )

1) Measure the voltage across the 2 metal contacts in the rear window, if there's voltage there, it must be because the demister is damaged.. (which it shouldn't be) If no voltage, continue..

2) measure the 3 contacts with the boot open, there's three contacts as you know, counting from left 2 right.. calling these contacts A,B,C, under contact A, there's a switch connected to a relay (?) and the switch must be pressed down for any voltage to reach A & C, (a sensor to know if the boot is closed to tell the car which brake light to use whether the spoiler light, or the top mounted light, and if the boot is not on/closed, then the demister won't turn on, you can check this by turning on demister, and check that the demister light on the dash comes on only when you press down on A) when nothing is turned on, A & C should earth, but I guess you don't need to check that, that means B is also earthed all the time (negative), from now assuming that the switch under A is pressed down, and engine is turned on, and demister is on, now if you get someone to step on the brakes, the voltage from A to B is approx +12v, but the voltage from C to B is -12v, this voltage is for the demister, if you don't have this voltage, check the fuse? (What else is the demister connected with? If it's the fuse, anything that's connected inline wouldn't work too, so fuse is less likely, unless demister has its own fuse, I haven't owned the EXA long enough to find out), and if it's not the fuse, then there's something wrong with electricals from the switch to these A,B,C contacts, so you should consult an electrician, now if the voltage is there, good, proceed..

3) now unscrew the 2 screws, and take this thing out, have a look at it, it has 3 wires connected to it in the back, disconnect the connector, and use a meter and test the continuity of this thing, the other side of this connector looks like this...

B -

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test that all 3 connectors are not shorted to any other, and test the continuity from this connect to the 3 pin side, the middle pin should correspond to the "B" pin above (also the middle one), now if there's no continuity, then it's probably this connector that you need, if all three pins gets to this connector without trouble, you can continue to test the other side of the connector, otherwise if you've got up to this point, then it's probably some wiring problem from the connector to the actual contacts behind the window, do the above first and tell me what you've got..

the problem with mine was, I've found the connector (the B pin) to be burnt black, probably due to previous overheating/overloading, and the other side of the connector (I think is the male side) is also burnt, and the plastic insultator has harden (after heating and cooling) and the contacts are covered by copper oxide (green) probably due to the overheating accelerating the rusting reaction, anyway, I've cleaned my contact and wires, all continuity ok, so I thought there can't be any problem, so I pushed the connector back in tightly, and assembled everything back, then I went back to step 1), and now there's voltage across the 2 contacts! (I think if viewing from the back of the car, the right side was earthed and the left side has -12v), so I took the car for a drive with the demister on (even though there's no mist) after few minutes, I feel the demister (stupid act =P), and YUP! It's hot~ Now if you don't want to be as stupid as me but still want to test it, then take your car out for a drive at a cold night, close all the windows, after 5-10 minutes, your car's interior glass will start to fog up, now you can turn on your demister to find out if it works! Tell me how you go with the above, and maybe your problem is just as simple as a previous overheating same as mine..

good luck,

cheers, Lewis

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Replying to Original Article:

Hey guys, I have a problem. The rear window defogger is not working. When i hit the switch on the dash, i can hear the relay click, but it don't work. The filament on the rear screen is intact. Has it got anything to do with that 3 way switch on the hatch that meets the boot? The one with the switches that "push" in on the inner surface of the hatch......I hope you guys know, cause its got me STUFFED.... thanks