Disco 1 300tdi heated rear window

Can someone please advise as I've looked at other threads but couldn't find anything quite the same. Problem I have is I don't think the heated rear window / heated mirrors are working. I say think because difficult to tell for sure in this warm weather. When I operate the switch (which I've tested) the relay (which I've tested) doesn't operate. No other non-working items, self test of mfu using the hrw switch doesn't start.

There appears to be two fuses involved, a 30 Amp fuse in the engine compartment fuse box which covers the high current side of things and a 10 Amp fuse (F 13) in the passenger compartment fuse board which covers the switching side of the circuit.
Since you've tested both the switch and the relay which I presume was successful, I would say that the problem probably lies in the MFU or the wiring around it; dirty contact on plugs and sockets.
I've given you two diagrams, the second is nothing more than just the two mirror heaters.

Very simple circuit, a single fuse no.1 in the the engine bay fuse box supplies the voltage to the window and mirror heating elements plus the switch bulb via the relay contact, the MFU switches the relay when instructed by the switch... if the lamp in the switch illuminates then the relay is operating.
In the main fuse board, fuse13 is the ignition feed for the MFU and fuse12 is the main feed to the MFU.

Testing the rear window element doesn't stop when the weather is warm, get your meter out and check for voltage at the element. Simples.

AS they say .... "A picture can say a thousand words"

Many thanks both, will take another look at the weekend. Incidentally the orange operating bulb doesn't light despite it being a good bulb

Incidentally that's a better diagram to follow than my Haynes manual, where is that from?

darland said:

Incidentally that's a better diagram to follow than my Haynes manual, where is that from?

Click to expand...

It's from RAVE for the Disco 1. downloaded from:- http://landroverforums.com/forum/general-tech-help-8/link-rave-iso-images-42972/
among other locations.

Thank you!

just to close this out - in the end it was a faulty control unit, the one that piggy backs onto the interior fuse box (under the steering wheel). Changed the unit for a second hand one and all good - thanks to all for suggestions