heated rear screen wiring question
 

I have a question regarding the wiring for the heated rear screen. As many of you will know I done a batch run of heated windscreens for our cars and am currently in the process of making 25 wiring looms for them. As one of the options, I'm thinking of setting up the wiring loom so that the front heated screen comes on when the rear heated screen is switched on, effectively running both off the same switch.

Now if I were to set up a relay enable to do this, I need to wire my trigger wire for the relay to a feed which would be live whenever the rear heated screen is switched on. Looking at the wiring diagram on Rave for the heated rear screen, the diagram shows that Pins C0662-7 and C0662-5 on the AC panel are part of the heated rear screen wiring and go to the BCU, from which C0660-14 goes from the BCU to the rear windscreen.

If i splice into either of these cables to run a feed from for the trigger for my relay, would it work? Are these two wires (C0662-7 and c0662-5 on the AC panel) only live whenever the rear heated screen is switched on?

Attached is the wiring diagram.

Any help will be much appreciated :)

Thanks,
Rick

Yes. Looks like run the relay in series off pin 14...
But would it be better to run when demist is active somehow..??

Cheers Pete.

Do you recon it'll work off pins C0662-7 or c0662-5 on the AC panel? Just easier to wire from the AC panel than trying to splice into the wiring on the BCU :)

Going to test those two wires with a multimeter tomorrow to see if they power up when the rear heated screen is switched on.

Does 14 not go straight to the rear screen relay in the engine fuse box??

What a faff, easier to just fit the parking heater IMO.

On a petrol?

LOL...


ooops :)

No Rick, it won't.
C0662-5 is the supply to the HRW switch illumination and C0062-7 is earthed when the HRW switch is operated.
I doubt it.
C0660-14 is earthed by the BCU when the HRW is activated so you need to wire your additional relay in parallel with (not series as Pete says) the HRW relay.

Check with a multimeter what is happening on C0662-7. Isn't the HRW switch non-latching, i.e. a momentary action switch?

Simon

The switch on the dash is just a pulse switch effectively just energising a timer to run the relay in the engine bay fuse box. From memory the wires you refer to are one an earth the other I think feeds the light on the switch. You may be able to run your relay off the lamp feed but I am unsure.
I had problems with the Tourers HRW about two years ago everything appeared to be working but there was no power at the screen or mirrors. I ended up retiring the whole thing from my auxiliary power supplies that I had run to under the steering column and mounting a new switch on the bottom switch panel where the seats and c/c are mounted. I am intending running the new front screen from the matching switch I mounted on other side of the same panel.
I don’t know how this batch will come but the last heated front window I fitted was a window of two half’s. Element one doing the drivers side and element two doing the passenger side the resistance of the screen suggested that each element would be pulling 22 amps at thirteen volts. For this reason I powered the two relays I fitted direct from the battery on a 6mm cable through a 50 amp flat bar inline fuse. Might be worth checking to see what way this batch of screens have been made and what the resistance of the elements are. I am assuming these will be the same and need two 25 amp relays one for each side.
I will discover when the screen arrives what will be required. Meantime I have two 25 amp relays fitted ready to go if it is just one element then I will need to hunt for a big enough relay to carry the load.
Hope this doesn’t confuse the issue further.
Alan
PS going down the local breakers yard to remove a screen for the MOT assuming autowindscreens haven’t been there first as I know they were pulling second hand ones as their source of new ones had dried up.


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:wot:
Thanks Alan; that’s my feeling too. It earths C0062-7 only for the time it takes to press the button. This terminal is not suitable for attaching a relay.
C0062-5 does feed the switch LED. I expect that it will be a supply capable of only a very low current and may well not be 12v. It would not be good engineering practice to attach a relay to this supply.

Rick, you should wire your relay in parallel with the existing HRW relay. As Alan warns, take care with selecting this component because it will need to be rated for a very high current indeed.

Simon