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Heated Screen Genuine Switch Conundrum...


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I know loads of questions have been asked about heated windscreens, so I apologise, but I can't find any threads relating to the use of a genuine switch. I originally asked this in my build thread but understandably not many people will see it who might know the answers.

Facts before we start:

This is a 2002MY TD5 Defender bulkhead harness without heated screen wiring.

I'm using the Vehicle Wiring Products timer relay to power a standard 70 amp relay for the actual screen.

Everything else about the wiring relevant to this is standard TD5 2002MY (even though it's a V8).

Below is a diagram that Nick Williams did, stolen from here. Unlike Nick's diagram, I'm using the genuine heated screen switch, which makes life slightly difficult as that's wired up differently on the factory heated seat loom (also below). I've tried to translate this by showing the equivalent colour wiring.

'Genuine' layout:

HFS1.png.463aafafe02a940a8e3ed1010fe49290.png

How my Frankenstein of the above translates to Nick's diagram:

HFS3.png.a0136b9a9da4622d78830d23a06d56ae.png

 

Pins as described in the 2002MY wiring diagram

HFS2.png.e73fa3b9225869e5647d57701f4b2ec9.png

How that looks in real life:

20200412_230409.jpg.92672c8408e08c4d2c205202d0efdb4e.jpg

 

So this looks right if I am interpreting these two separate diagrams correctly, but I'm getting some odd behaviour from the switch. Obviously pins 1 and 5 are the most critical, and they don't work if you swap them around. When only the wires on 1 and 5 are present, the switch operates - the relay is energised, screen comes on and goes off on timer or when the switch is pressed again. The telltale doesn't work and it doesn't illuminate with the lights, as you would expect with just those two wires.

If I have the earth on 4 and illumination feed on 2, as per the 'genuine' way of wiring it up, it completely changes. The telltale is always on, the switch illuminates with the lights only with the ignition off, and the switch absolutely will not activate the relay. The biggest issues appear with the earth connected. I have made sure the connectors are isolated and not touching, the photo is misleading.

I have checked my wiring with a 3 pin on-off switch just to make sure there wasn't a problem with my harness for the screen and it works perfectly, including the earth. The pins match the intended operation (if not the layout) for the diagram. So what am I getting wrong?

This has been holding me up for about 3 weeks so I'm getting pretty desperate!

Edited by ThreePointFive
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Thanks Maverick, that changes a few things on my layout but now it's blowing the fuse on the ignition-switched positive feeds. I'm starting to suspect the switch hasn't survived the previous attempts so have ordered another. If that doesn't solve it, I will build the harness again from scratch using your diagram from the start this time.

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  • 3 weeks later...

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