Electrical Mystery....

[DurtyDisco]

All,

I have an electrical mystery on my 96 Disco Commercial I need help with........sometimes everything works and sometimes I get some or all of the symptom's below.

I have numerous electrical problems, non of which seem to be realted but must have a common link.... I just can't think or work out what it is....

Interior lights stay on.... but all door, bonnet and rear door switches are working fine, you can switch the light off in the passenger cabin with the switch but the load area and rear light near the rear door door stay on, so you have to take the bulbs out.

Lights on alarm when you get out and leave the lights on doesn't work.

Rear heated screen doesn't work

Rear wiper doesn't work

Alarm sometimes works, sometimes doesn't.

Reversing lights stay on permanently (despite changing the mechanical switch into the back of the gear box.)

Glow plug indicator light in the binnacle doesn't work, (maybe the bulb as we have had the binnacle apart sooo many times though!) To be checked.

I've been over the truck for three weekends, all the earths are good, I am getting live feeds where I should be, but things just wont switch off....

Short of re-wiring the whole thing this is doing my effing head in! and I'm flummoxed..... along with two experienced auto electricians who've had the truck apart with me!

The next job will be to start pulling multifunction relays apart, but at £90 + VAT a throw I'd like to avoid this.....

Has anyone else experienced conditions like these..? In part of as a job lot.....

Cheers

Andi

[minty]

 :-k does it seem to happen more after when its rained? i had part similar problem with tic tacs car ref rear lights and interior lights turn out to be earth wire to lights rear near side! and have you checked the battery condition as it can also play a part even tho it starts the car and you can use some of the electrical stuff if its on its way out it could be choosing between wot it will and wont let you use, this is common on old ford escourt cars. just an idea might not be the answer but well worth a look

[Evilgoat]

Can be bothered to edit the post so replies inline :) Have diagrams in front of me...



>Interior lights stay on.... but all door, bonnet and rear door switches are working fine, you can switch the light >off in the passenger cabin with the switch but the load area and rear light near the rear door door stay on, so >you have to take the bulbs out.

The Switches in the doors are connected between the lamps and earth, and earth short, eg any of the black wires suppying the lamps will cause this.



>Lights on alarm when you get out and leave the lights on doesn't work.
See up, possibly caused by faulty door switches, the suzukis sometimes doesn work and a swift boot to the door sill where the switch lives sorts it for a week or two :)


>Rear heated screen doesn't work
There is a relay to check here, make sure the rear window foil is getting power and that fuses  are intact. This seeems to earth in the door. If you arent getting a light to say its on then check fuse B3

>Rear wiper doesn't work
Could be a bad earth with the above related. Check with a mu;ltimeter between clean metal on the door and somewher eon the body (Seatbelt mount?)

>Alarm sometimes works, sometimes doesn't.
God only knows :) See link in jokes and funnies and ask :)

>Reversing lights stay on permanently (despite changing the mechanical switch into the back of the gear box.)
Earth fault on cluster is unlikely, theres nothing to earth to, this implies a wiring fault as they are switched +12v rather than earth, damaged harness. The sinking feeling is back again...

>Glow plug indicator light in the binnacle doesn't work, (maybe the bulb as we have had the binnacle apart sooo >many times though!) To be checked.
Bulb I would guess, check glowpugs get power and timer relay on the bulkhead.

>Short of re-wiring the whole thing this is doing my effing head in! and I'm flummoxed..... along with two >experienced auto electricians who've had the truck apart with me!

>The next job will be to start pulling multifunction relays apart, but at £90 + VAT a throw I'd like to avoid this.....

Looking at the diagrams I have, on the post 95 ones the multi funtion unit looks like the only common thread. Explains lights, Heated rear window and possibly alarm. Reversing lights are still manual though, its possible a fault in the trailer socket could be to blame looking at this.

The rear window demister could easilly be overriden by the looks, theres a realy somewhere that simply turns it on and off at the command of the lutli function unit, a switch replacing the fee would override it. I would imagine the rest could be overiide.

Fact its intermittant may point to these modules too :( Hence the sinking feeling.

[Ricky]

Some of the problems your having could be down to the multifunction unit, but not all. heres how to put the MFU into diagnostic mode.
A rundown of the components and tests for the MFU:

MULTI–FUNCTION UNIT (MFU)

CIRCUIT OPERATION
Multi–Function Unit (MFU)
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
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.
Hope this helps

[Ja1983]

^ Damn hes good!

i recon the problem could lie in shorts on the lights, or possibly as above... my option is the cheaper one, so i`ll continue!

My Fourtrak had issues with rear lights.... it was all or nowt, or every now and the a mad fit.... problem was the back of the bumper lights are right behind the wheels, so you can imagine what happened to them on wet days - wet electrics! and from thi oxidised contacts...

on o nicer day, i removed the units, claened them down, and sprayed WD40 all over. no problems after!

wont do any harm cleaning off the contacts (door pins also got cacked up!) and a chance before having to spend money!

good luck!

[Evilgoat]

Looking at the diagrams I cant see any wayt fo some of these symptoms to be earth related.

The reversing light earth feeds the stop lights too, youd see issues there. that one I *am* intregued about.

That diagnostic mode may be your answer though, Meter out each circuit and look for the system activating. May not give you the answer you like but it WILL rule it out. If any system doesnt activate, check the drives leaving the MFU to see if the MFU is calling for that circuit to be energised.

[DurtyDisco]

Cheers all, looks like the common thread could be the MFU........ more effing expense! The earths, lived feeds etc have been checked, the rear demister has been checked and is getting juice when the MFU and Binncle Switch are bypassed.

So another weekend of fiddling!

Cheers

Andi