Rear Heated Screen - No Power at Switch?

Hello,
Time for an old classic thread! I am getting there with my disco, and I have searched and read lots of threads etc but I cannot find the solution to this problem, so any help is much appreciated.

1996 Disco 1 300tdi 5 door.

The rear heated screen is not working, the light on the button is not working either and I cannot get it to go into Diagnostic mode for the MFU?! I hope to fix all this before winter.

Other things I can confirm:

• There is no power to the Rear Heated Screen switch using a 12v test light. - Does this come from the MFU or can I trace the wire from something else?
• There is no front heated screen on the vehicle.
• The key beeping, wipers, and rear wiper work. As did the rear fogs last time I checked.
  
• The front washers were removed at some point in the vehicles life.
• The interior light only works in the on position, not with the door open.

So any suggestions please? Many thanks

Richard.

Have you checked the fuse?

discool said:

Have you checked the fuse?

Click to expand...

Yes, although I was having problems with an old test meter at the time. Now you mention it I cannot remember if I have tested (with the new 100%) meter if there is 12v at the fuse....

However the fuse is fine.

Did you check for voltage between the pins of the switch's plug or against earth? ...cos it's important what is missing there the live or the earth if you see what i mean, anyway the feed(for the swicthed contact and bulb) are supplied by the MFU through the relay also the relay coil's feed is from the MFU as well, remove the relay and bridge it's contact see if the switch illuminates or not

btw, which fuse did you check F1 engine bay or F13 fascia fusebox

sierrafery said:

Did you check for voltage between the pins of the switch's plug or against earth? ...cos it's important what is missing there the live or the earth if you see what i mean, anyway the feed(for the swicthed contact and bulb) are supplied by the MFU through the relay also the relay coil's feed is from the MFU as well, remove the relay and bridge it's contact see if the switch illuminates or not

btw, which fuse did you check F1 engine bay or F13 fascia fusebox

Click to expand...

I tested the switch against earth.

I checked the earth on the foot well and that seemed in (surprisingly) good condition. I tried another relay, but did not bridge the contact, that is a good idea.

I assume if it is dead, it could be the MFU, as you have kindly answered that this is where the power comes from?

Thank you for taking the time to reply, its really appreciated.

Quick update to this.

I have at last got around to double checking Fuse No1 in the engine bay, this has got power so no problems there. So I assume its the MFU on the fuseboard, tomorrow I will give this a look and perhaps a spray over with contact cleaner, failing that I guess I will need another....

What about F13 fascia fusebox?