Disco 1 Electrical gremlins

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Well, I put in the black MFU and ..........................................................same symptoms occur :confused::confused::confused::confused::confused: I can confirm that the rear fogs stay on regardless and there is loss of the rear wiper, but every other function does work as it should with the other cream coloured unit. So I'm still left with interior lights & red ignition light constantly on :mad::mad::mad:

I've checked the rear or (boot) door electrics for any chaffed wires but to no avail, everything is in good condition to be fair. Looks like now I'm gonna have to take the roof lining out and look behind there :rolleyes::rolleyes::rolleyes: There must be a short SOMEWHERE??????????????????????
 
Jasonmichael said:
Well, I put in the black MFU and ..........................................................same symptoms occur :confused::confused::confused::confused::confused: I can confirm that the rear fogs stay on regardless and there is loss of the rear wiper, but every other function does work as it should with the other cream coloured unit. So I'm still left with interior lights & red ignition light constantly on :mad::mad::mad:

I've checked the rear or (boot) door electrics for any chaffed wires but to no avail, everything is in good condition to be fair. Looks like now I'm gonna have to take the roof lining out and look behind there :rolleyes::rolleyes::rolleyes: There must be a short SOMEWHERE??????????????????????
Click to expand...
Would it thus be fair to say that the black MFU does not work as expected? From reading your posts it seems as though that is the case, ( I'm being cautious )....
If so, then I would agree that the fault is exterior to the MFU.
You mentioned in a previous post that the rear wiper had stopped working - do you recall what you were checking / moving around etc., at this point - as it might be worth another look in the same area....
 
The black MFU DOES do exactly what I expected it to do, in that the 2 things I expected to be different (fogs lights constantly on & loss of rear wiper) were true. Everything else was the same as the cream unit functionality wise, (including the damned constant interior light fault & ignition light) so ruling out either one of the MFU's being at fault. Therefore back to my wiring diagrams and short circuit chaffed wire thinking :rolleyes:
 
Jasonmichael said:
The black MFU DOES do exactly what I expected it to do, in that the 2 things I expected to be different (fogs lights constantly on & loss of rear wiper) were true. Everything else was the same as the cream unit functionality wise, (including the damned constant interior light fault & ignition light) so ruling out either one of the MFU's being at fault. Therefore back to my wiring diagrams and short circuit chaffed wire thinking :rolleyes:
Click to expand...

Mmmm. But we expected the courtesy lights and ignition light to go off, with the black MFU, which they didn't.....
 
I've just done myself a front to back electrical wiring easy to read / use electrical reference from each relay to switch to component. Good job I ain't colour-blind. o_Oo_O
 
I will do.........if & when I can see it actually works. Don't wanna be responsible for turning anyone elses Disco into a 'Disco' :):):)
 
Done a little exploration work this aft, started with taking a fuse out, one after another to see how it affected matters. Now when I got to the interior lights, clock, radio and trailer lights fuse, I pulled it and the interior light died but the radio and clock flashed on & off when the HRW button was pressed and also the ignition light????
With the ignition on, the radio worked and the clock went out????

Beginning to think this car's possessed!

Radio out tomoz, have a look behind there, whats going on. Just thinking about it, I've just been through loads of old paperwork I got with it and one new thing that I'd noticed was just before it went 'off the road' for a 5 year sabbatical, it had a new tow bar fitted, I wonder if whoever fitted it cocked up the electrics?????
 
Thank god for old paperwork.
The LR kit for the towbar electrics was relatively dear at the time, but brilliantly simple plug and play..... so if it has this genuine set up, it should just unplug.....
if some tight person has scotchlocked it all together = OMG:eek:o_O:confused::mad::mad: and it probably needs a rework anyway, so I'd agree, this could be good place to be looking:)

Good luck:)
 
Oh well, another theory out the window! All towbar electrics are ok, no shorts, no chaffed wires. This is starting to do my head in now:mad::mad::mad::mad::mad: Had the fuse box out today too, a little green corrosion but nothing that would cause that fault. Put it all back together, no change. Got another trick up my sleeve tomorrow, hope this one works :rolleyes: At least there's one think, i'm getting to know Discovery electrics like the back of my hand..
 
Had another fiddle today, not cured it BUT!!!!!

I thought balls to it!!!! What would happen if I took out the MFU completely??????

Well in the interests of research (again) I did that, powered up the battery and..............everything works??????? Well when I say everything
Side lights, headlights, main beam, front fogs, indicators, hazzards, central locking, alarm, electric windows, cruise, heated seats, dash illumination, blower fans & air-con. Everything MOT-able :D

The only circuits that don't work are HRW, HFW, rear fogs. Interior illumination STILL BLOODY ON! :mad::mad::mad::mad::mad::mad: if left in the middle setting??? But the ignition light is permanently off.

Hypothetical question What does the MFU ACTUALLY do??? AND if I left it off what detriment would it have on the truck????

The interior light circuit is now shouting out to me that somehow there's a permanent live somewhere, but I'm buggered if I can find it. I've scrutinized all the Haynes book of lies wiring diagrams and there's a Purple & Brown wire constantly live on the interior light which is causing havoc with the interior lighting feed. :(:(:(
 
MFU controls all the time delays such wipers and washers, heated screens plus headlamp being ON for the rear fogs lights to work light, lights-on and key-in switch beeper, dim dip control and operating the electric drivers seat with the ignition being on when opening the door ... info on that is in the owners handbook and the alarm and oil pressure warning light also interfaces with the MFU.

There is a permanent 12v live to the interior light fittings as standard, that's the purple-brown wire.
Purple-blue wire is the interior lights grounding wire back to the MFU enabling MFU to control illumination when unlocking and the illumination time delay, so isolalate that wire from the light fitting and see what happens.
 
Last edited:
discool said:
There is a permanent 12v live to the interior light fittings as standard, that's the purple-brown wire.
Purple & brown wire is the interior lights grounding wire back to the MFU enabling MFU to control illumination when unlocking and the illumination time delay, so isolalate that wire from the light fitting and see what happens.
Click to expand...


I dont think so ;) - aint it a black wire that earths?
 
The Mad Hat Man said:
I dont think so ;) - aint it a black wire that earths?
Click to expand...
Ok correction, it's the purple-blue wire that that runs runs back to the MFU.

Yes it is the black wires that are earth, but there isn't an earth involved yet untill the MFU decides to make that connection via information from a couple of of inputs therefore the purple-blue wire is simply a link wire.. Simples.:)
 
Right now, not been able to do much recently but today -

Cut the Purple & Blue wire from C205 plug to the MFU, and the interior & the ignition key lights all went out. Performed all functions of the MFU manually and everything worked apart from the interior lights & ign light (obviously). But no rear washer working???? Now I'm of the mind that possibly a door switch could be faulty??? o_Oo_Oo_O Now I know that the drivers one works because when I leave the key in or the lights on I get a 'BONG' from the warning.
This is confusing because I checked all the door switches and replaced them because they were manky, cleaned up the earth points too, unless there's a wire broken somewhere??? Looking at the wiring diagrams it seems its spliced into the alarm somewhere??? God knows where???

Do you think I'm on the right lines here??? In that a wire / connection /switch or splice could be the problem???? or even the alarm unit??? I'm sure now its along those lines as theres something fooling the doors into thinking they're open, keeping the lights on and stopping the rear wiper from working????
 
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