Thread: Rear Window defrost / defogger Disco 1

Not 100% clear about what the problem is, but sounds like rear window defroster element is intermittent.

If this is correct, first question is do the side mirrors work?
When you hit the rear defrost switch for the rear window, the mirrors also have defrosters too, so they also switch on.
Is it just the rear window, but the side mirrors still work?

if this is the case, then there are a few connectors from the switch/relay to the rear element, and sounds like one of those connectors are intermittent, or the rear window element itself is dodgy.

If rear element AND side mirrors don't defrost, then it could be dodgy relay or even dodgy fuse holder(if the fuse itself isn't loose or whatnot).

Your location says US, and my RAVE electrical library doesn't cover NAS too well. It does in some parts, but not all.
The relay is located in the engine bay fusebox.

My Disco 1 is configured with separate push switches for rear Window defrost and side mirror defrost. That said, both defrost are not working. I'll attempt to locate relay and inspect fuse holder. (Rear element and connections test ok). If anyone has a resource for a wiring that would be awesome.

Originally Posted by Trilowe

My Disco 1 is configured with separate push switches for rear Window defrost and side mirror defrost. That said, both defrost are not working. I'll attempt to locate relay and inspect fuse holder. (Rear element and connections test ok). If anyone has a resource for a wiring that would be awesome.

Fuse holder and fuse are good, anyone know where the relay is located and what controls the relay? Also radio volume up and down not working.

Strange that it has separate switches for rear window and side mirrors.

Can't find that setup in any of the RAVE manual pages that I have.

RAVE is the LR workshop manual for their vehicles.

You said that rear element appears good, connections test ok.

Did you do a continuity test across the element?

Have you tested the ground?

Noting that you have two separate switches to deal with ...
The relay for the rear screen should be passenger fuse box on the fusebox(as described in RAVE)

Is there a possibiility that a previous owner has modified the system to include a separate switch for the side mirrors?
That is, is that switch std LR switch, is it marked side mirrors, is it just a dodgy aftermarket switch added inline to the rest of the system as a passthrough and it's burnt out or something.

Also note that it could be any one of about 6 or 7 connectors mid way along the system.
RAVE-elec-rear screen.jpg

Screenshot of the electrical diagram.
Note the number of connectors on both the power(NP=brown/purple) line, which turns into a black line at some point on the rear element, and also note how many connections on the earth line too, all black wires.
Common sense would say that if it were a connection issue, and mirrors and rear screen not working in this system, you would test from S237(junction) for any breaks in the wire back to the fusebox and it's connector(C211).

Of the RAVE manuals for electrical, there are 3. This one is the 1996 version, the other two are 1995(I can't see much difference) both for LHD, and there is one for RHD. All three show the single switch as shown here(X132).

I have tested rear screen element and grd. All test a solid ok. Where is the MFU located? Thinking this could be the culprit? I have an electrical engineer back ground so if I can locate the MFU I might be able to repair. Tere have been no modifications to the system.

From RAVE:

The multi–function unit (MFU) is mounted on the
rear of the passenger compartment fusebox and
has an input to operation of the following:

Heated rear screen

Courtesy lights

Side and headlights

Rear fog guard lamps

Headlamp power wash

Front wipers

Rear wash/wipe

Also from RAVE:

Diagnostic Procedure
1.
Close all doors and the tailgate.
NOTE: If the oil pressure switch goes open
circuit (engine is started) during the following
procedure, the MFU will exit the diagnostic mode
immediately.
2.
Press and hold the heated rear screen switch
and switch on the ignition.
3.
Release the heated rear screen switch within 2
seconds and the MFU will beep to indicate that it’s
in diagnostic mode 1.
4.
Press the heated rear screen switch; the MFU
will beep twice. In turn, operate each of the
following switches, rear fog guard lamps, side
lights, headlights, front wiper, and rear wiper. The
MFU will beep twice each time a switch is
operated.
5.
Pressing the heated rear screen again will
cause the MFU to enter diagnostic mode 2.
6.
The MFU will provide outputs to the following in
order given below:

Heated rear screen relay energised for 2
seconds

Courtesy lights energised for 2 seconds

Dim dip relay energised for 2 seconds

Rear fog guard lamp energised for 2 seconds

Headlamp power wash energised for half a
second

Front wiper energised for half a second

Rear wipe/wash energised for half a second
7.
The MFU will then exit the diagnostic mode.