Heated front windscreen wiring

[paulsco]

I have just fitted my new heated front windscreen to my FHC; not easy.

The connections are at each side of the screen, exactly where the brackets are for the dash top.
This definitely could do with a re-design.

Anyway; I was thinking of wiring it up to the heated rear window circuit, so that they are both operated from the same switch. I don't really want an additional switch unless absolutely necessary.

I will probably provide the current through a relay as the information on the windscreen indicates that the draw is 12A and I think I have read somewhere that the rear draws 15A.

I just wondered if you thought that this was a good plan or if you could see a problem with this approach.

Thanks,

Paul

[mgcjag]

Hi Paul...dosent sound like a good idea to me having both on the same switch....first you will be pulling too much current through the same switch..unless you say incorperate a relay.....but you would have to switch both on at the same time when for example you only needed the rear on......Steve

[cactusman]

Steve is right. Too much current for the switch and probably too much for the existing switch cables too.

[paulsco]

Hi Steve and Julian,

Yes I think Steve is right too. I think I will have more control if I wire them separately.

I don’t however think wiring them off the same switch would have been a problem.

I was going to wire them both separately off a relay and simply use the switch to well.. switch it on.

Thanks for your input. It is always good to get someone else’s point of view.

Paul

[mgcjag]

Hi Paul...you could probably set it up so that you use the warning light of the rear screen when either or both are on...and just a seperate switch for the front....Steve

[paulsco]

Nice idea, but I am not quite sure how I would wire that without the power tracking to both circuits?

Paul

[kingzetts]

Diodes in the feeds to the warning light to prevent reverse flows ought to do it.

[paulsco]

Hi John,

I'm ok with electrics, but not so much with electronics. Is there a particular size or type I should use?

Thanks,

Paul

[mgcjag]

Hi Paul..something like this should work..however a bit of a rework around the existing heated rear window relay will be needed...the relay is only there to switch in a resistor to dim the warning lamp when the side lights are switched on.......

[kingzetts]

Paul,
I’m very far from being an electronics expert either. It was the one science subject I could never get my head around at school. But.....

The circuit below should work, and is a lot simpler than trying to use relays. The diodes allow current to flow to the lamp from either switched circuit but prevent current flowing to one circuit from the other. The diodes will be tiny, about the size of a solid state resistor,and if bound up in the wiring will be invisible.



Semiconductor diodes come in thousands of ratings. You want a basic diode, or a Schottky diode, with a maximum reverse voltage rating of well above 12V and a maximum forward current rating sufficient to carry the current to the warning lamp (I would guess anything above 1amp would be sufficient). They will cost pennies - if you have an electronic store anywhere near, pop in and explain what you want to the spotty youth behind the counter. If not, I’d think a couple of standard 1N4001 rectifying diodes would be fine, such as eBay item number 231206241455.

[paulsco]

Thank you Steve and John, I really appreciate your efforts.

Now I just need to decide where best to mount a switch without it looking too obvious.

Regards,

Paul