D2 Electrical Gremlins.

[Back in the fold.]

Hi All,

Hopefully somebody might be able to help with the following, I'm getting to the end of my tether having spent 8 hours stripping parts off my Disco to no avail.

Symptoms;

Loss of the following functions;

Rear fog light

Rear wiper

Remote central locking/unlocking (not alarm function though)

Central locking from internal switch

Indicators (dash light still works but no external lighting)

Now the strange thing is all functions work normally when the front wipers are on.

The internal fuse box has a large yellow relay (R3) this clicks when some of the functions are pressed and they don't work.

Any clues?

So far I've done the following;

Stripped out towing loom (dodgy wiring)

Stripped out old car phone set up.

Checked fuses

Checked front wiper earth & wiring.

General nosey around earthing points and wires. All in good nick with no corrosion.

I'm going to try and remove the fuse boxes tonight for a closer look, especially the internal one.

Under pressure as we need to get to Wales this week-end in it!

Any hints or clues appreciated.

[sierrafery]

You-re on the good road checking the internal fusebox/IDM ... next step must be the BCU/it's plugs behind the glovebox, water ingress there is quite common, or dry joints inside of the unit...or faulty BCU or IDM in the worst case... coz:

The BCU uses solid-state microprocessor control to perform logical operations and timing functions for a variety of

the vehicle's electrically operated systems, these include:

Door locking.

Anti-theft alarm and immobilisation system.

Exterior lighting including direction indicators and hazard warning lamps.

Courtesy lighting.

Wipers and washers.

Electric windows and sunroof.

Heated windows.

The BCU communicates with the IDM to provide the control signals to perform power switching operations in

conjunction with dedicated relays.

IDM

The IDM is integrated into the passenger compartment fuse box, which is mounted behind the fascia below the

steering column. There are no harnesses between the fuse box and the IDM. The IDM performs the power switching

operations for several of the vehicle's electrical systems.

IDM outputs

The IDM receives the following signals from the BCU using the serial datalink to provide power outputs:

Description Signal type System

Unlock all doors enable Digital Locking/ Unlocking/ Alarm

Lock passenger and rear doors enable Digital Locking/ Unlocking/ Alarm

Superlock all doors enable Digital Locking/ Unlocking/ Alarm

Lock driver's door Digital Locking/ Unlocking/ Alarm

Rear fog lamps enable Digital Exterior lighting

Daylight running lamps enable Digital Exterior lighting

LH direction indicators enable Digital Direction indicators/ Hazard warning/ Alarm

RH direction indicators enable Digital Direction indicators/ Hazard warning/ Alarm

Gear position indicator illumination Digital Illumination

Headlamp main beam indicator disable Digital Illumination

Front wiper enable Digital Wipers and washers

Rear wiper enable Digital Wipers and washers

Rear window enable Digital Power windows

Shift lever solenoid enable Digital Automatic gearbox

Transfer box solenoid enable/ Alarm sounder

relay

Digital Gearbox

Heated rear window enable Digital Heated screens

So as u can see it's quite complicated... seeing those inputs/outputs u figure it out where the problem lays. The best woud be to get hold of a known good fusebox/IDM and swap it with yours for test, just take into account that:

The IDM communicates with the BCU and the instrument pack via a serial interface. If the BCU or the IDM is replaced,

the communications link between the two units has to be re-established. This can be done either by switching on the

ignition and leaving it on for five minutes, or by using TestBook. The vehicle immobilisation will remain active until the

communications link between the BCU and IDM has been re-established.

Good luck

[Back in the fold.]

Thanks for the prompt response Sierra - much appreciated.

Luckily I've solved it!

After removing both fuse boxes for a closer inspection I noticed a spot of blue oxidation under the engine bay fuse box.

The main loom (about 2.5" diameter) had a pin prick through the outer tape and the top wire (purple with brown? tracer) had corroded.

Once I'd stripped it back the wire was totally corroded through. I rigged up a test wire and everything was working again.

Soldered in a new bit of wire and all is good.

Now just got to put all the bits of removed trim back on!!!

I'm a bit perplexed as to how the wire corroded as its totally shielded by the fuse box so nothing could have accidentally broken the insulation.

I'm just glad that the wire was in a fairly visible & accessible place!!

Anyway, happy days.

Thanks again.

Sandy.