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Heated rear window

I love the heated rear window!  My Etype didn’t come with it originally but I was able to find one along with the wiring harness and new dash indicator strip so it would look original. It comes in handy when its getting cold and the rear window gets frosted up. I don’t usually have mine out when it’s snowing so that hasn’t been much of a factor here in Michigan but on cold nights the back glass fogs up and its very handy to have.

 

I had a problem a few years ago, I was checking my lights before a car show and all of a sudden my interior was filled with white smoke!  I’m still not sure what happened but I figure something shorted out. Lucas, go figure!  It burned the main power wires to the rear window harness. So now I’m going to replace the harness. I originally used a Radio Shack relay instead of the usual Lucas type. So now I’m looking at putting everything back to original and wondering about the Lucas relay. For some reason, the relay for the rear window says “incorporating resistance”.  What? I’ve never heard of that! What are they talking about?

I’m not an electrical engineer but I’m pretty good at that stuff so what exactly is going on here?  The Jaguar wiring diagram is not the easiest thing to figure out

Jaguar etype heated rear window

wiring diagram for the etype heated rear window

 

I always thought relays were used for electrical connections where a switch was not capable of handling the amount of power used in the circuit. You use the switch to power the relay and the relay contacts can handle the load. The wiring diagram for the etype doesn’t make sense. As you can see from the wiring diagram, once you flip the switch the power goes straight to the heated rear window. Flip the switch on and BW wire gets power, its goes to C2 on the relay and then onto the window. Whats the relay there for?

 

Well, it turns out the relay is there to dim the indicator light at night. Yep, that right, that’s all it does! In the daytime the indicator light on your dash will be bright yellow when you turn on your driving lights, power will be put on the W1 side of the relay. This will open the contacts in the relay running the power thru the Lucas #33285A relay which has a resistor built in and this lowers the voltage going to the indicator light thus dimming the light for nighttime use.  Pretty smart.

If you are not worried about your indicator light dimming, you really don’t even need this relay. A new relay of this type can be kind of expensive, an alternate idea would be to get a normal relay and add a 50-ohm resistor between W1 and C3. Or just pay the $100 and get the right relay.

 

The Lucas 33285A relay is a normally closed relay, with resistance and should only be used in this circuit, it is not a substitute for other relays.

 

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