OK, just bought a heated screen and put it on the car. I am wondering whether to connect the heater bit, but not sure what actually is needed. I have
a spare switch on the dash which is currently connected to the engine fan *just in case* but I've never needed to use it. Do I need a relay for a
heated screen and, if so, how would I wire the thing into the loom?
Any help gratefully received.
Simon
First thing it to probably connect it up across 12v and see what current it pulls with a multimeter. That'll fundamentally specify whether you can use a loom connection or a seperate relayed supply. If you haven't got a multimeter try connecting it via various ampage fuses (ie 1A, 3A, 5A). That'll tell you approx what ampage is being pulled by which ampages blow!!)...
Another point to consider is a timer circuit.... so it doesnt stay on for too long.
My mondeo has timer circuits on both screens.
I'd recon you'll need 25amp circuit which means a relay !
Tintop HRW are always wired through a relay
OK... so it looks like a relay is needed. How to I actually wire it in (in simple terms): wire from a fuse to the relay to the screen? wire from the other side of the relay to the switch? + earths?
When I stripped my sierra ghia donor, the wires to the heated front screen were the thickest I have ever seen on an automotive circuit that did not
involve a starter motor!
BIG relay required
Thanks peeps
Just called Caterham to say I had got a heated screen s/h from "another owner" 
and what rating relay and fuse do I need to fit?
Parts Dept said "dunno" and put me through to Engineering, and the answer is... No relay (!) and just a 10A fuse.
I have to say that the wires coming from the sides of the screen don't look particularly thick, so maybe (hopefully) that is correct.
Has anyone else got a Caterham heated screen and can confirm/rebut this?
Guess they just use a beefyish switch instead.
Yup, I'm running a Caterham heated screen, and no I don't use a relay. It hasn't blown a 6 amp fuse yet, so I wouldn't worry
quote:
Originally posted by Marcus
Yup, I'm running a Caterham heated screen, and no I don't use a relay. It hasn't blown a 6 amp fuse yet, so I wouldn't worry