Disco 1 Electrical gremlins

My 1997 V8 Disco has developed an annoying habit. The interior lights keep flickering into action when the doors are shut??? I thought it maybe the door switch buttons at fault so I replaced them all, but its still doing it. so much so they now stay on even when locked and flatten the battery.

Doors closed and locked with fob, therefore alarm active = the interior lights front rear & boot off. Leave it for 10 minutes and all the interior lights start to flicker, dimly at first (like the bulbs are on the way out) then come on constantly.

Blip the fob, doors unlock, open the door, any door and the interior light if not already on, comes on. Get in the truck, shut the door and the interior lights stay on.

The manual switch in the roof works perfectly in all 3 positions.

So far I've chased all the relevant door switch earths, give em a good clean. Replaced all the door switches, taken apart all 3 of the interior lights and cleaned the contacts and re-built them. Rear wiper works fine. Put them all back together and I still get the same symptoms

I disconnected the alarm siren ages ago as it started to self combust due to the internal batteries leaking, but the alarm seems to still work correctly in that if you breach it the indicator lights start to flash.

Today -

Connect battery (sick of it going flat) - interior light is on constantly, when its in the middle position i.e. left to its own devises coming on when you open door or blip the alarm to open. This along with the red ignition light. Put the key in turn ignition on, there's no change. I tried to do this diagnostic thing with the MFU to check all the MFU circuits but it won't initiate.

Strange thing is with the ignition on if you press the rear heated screen switch and keep it pressed in, the interior light go off??? As soon as you release the button the lights come back on

I'm pretty useless at electrics, however I've been looking at the wiring diagram in the haynes book of lies and the interior lights & rear heated screen share an earth, could this be the fault in that there is a bad connection to earth?

Bet you have a chafed wire getting to earth.

Hmmm, which circuit would I be looking at for that Pete, the interior one or the rear heated window one????

In my very limited knowledge looking at the wiring diagram, the interior lights & the heated rear window share the same earth, I'm wondering if it could be there somewhere??? The diagram shows E11 as the earth anyone know where that is???

pete1987RRC said:

Bet you have a chafed wire getting to earth.

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+1 - Most electrical gremlins are, IME, related to one circuit trying to earth through another, and this seems to fit with your experience here.... ( and they can be a PITA to find too ). I try and keep an eye on all my earth straps as part of servicing - taking them off occasionally and cleaning and coating them with vaseline.

Given that the HRW wiring is moved about every time you open the rear door, I would start there and see what you can find - IIRC, that's also quite easy to do as the "rubber tube" can be de-installed quite easily - especially so if you take off the rear door card.

You could even hold the rear door switch "shut" ( with tape, or a glamorous assistant etc... ) so you can move the door about and see if you can find a sweet spot ( where stuff works as intended ), and go from there.

If it is the MFU, IIRC, they are cheap enough on the bay of fleas...

Good luck with it

Thanks for that Disco1BFG, don't wanna sound thick (trying my best) whats HRW??? And when you say 'rear door' am I right in thinking the boot door???

If its the MFU they're bloomin expensive, mines the cream one not the black one :-(

Multi function units are expensive, I paid £130 to Rimmer's for one back in 2012, and now over £200 I believe.
You could try a breaker but like all s/h electronic equipment u don't know how long it will last, and if yours is the original so an 18 year old unit was doing well bearing in mind it's a bit of electrical kit that is powered up 24/7.

The MFU control a few things it's rather spooky the way those items work on their own when in dianostic mode, but as u can't get that facility suggests there may be an issue with the unit.

Do your rear fog lights work or the front and rear wiper still have their delay facility? All the switches on the door do with regard to the interior lights is to signal the MFU to switch them on.

All the other individual circuits work - Rear fogs, rear wiper, intermittent front, front heated window, lights etc..... its just the interior lighting timer delay. If you put the sitch on the constantly 'off' position that works fine, constantly 'on' works fine, leave it in the middle setting - constantly on. Red ignition light on all the time. turn on ignition press rear window heater in & keep it there, interior light & red ignition go out?????

Jasonmichael said:

Thanks for that Disco1BFG, don't wanna sound thick (trying my best) whats HRW??? And when you say 'rear door' am I right in thinking the boot door???

If its the MFU they're bloomin expensive, mines the cream one not the black one :-(

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HRW = Heater Rear Window

Apologies about the MFU - last time I looked, admittedly second hand, they were going for teens of £'s - now hundreds =

(didn't even know there was a cream one - all mine have been black!)

Jasonmichael said:

All the other individual circuits work - Rear fogs, rear wiper, intermittent front, front heated window, lights etc..... its just the interior lighting timer delay. If you put the sitch on the constantly 'off' position that works fine, constantly 'on' works fine, leave it in the middle setting - constantly on. Red ignition light on all the time. turn on ignition press rear window heater in & keep it there, interior light & red ignition go out?????

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ref your other post - yes I mean the rear "boot" door - the one with the HRW and wiper etc...

More i hear - more i think earth fault on the shared earth circuits.

Well, after checking as much as I could today I think I've come to the conclusion that the MFU is FUBAR. Tried allsorts today checking as much wiring as I could & as many earths. Then as I was scratching my head, after putting everything back together and checking it worked as before, the rear wiper wouldn't now work???
So now I have interior lights constantly on, ignition red light constantly on, no rear wiper now

So, my plan is to get a temporary AMR 1280 (the black one) I know there will be differences i.e. no rear wiper or rear fogs, just to see if there's any improvement at all (if it cures the interior lights / ignition problem). I'm told it does everything else interior light,headlight washers,intermittent front wipers,heated front & rear screens,headlight on buzzer, glovebox light and the light around the ignition barrel. BUT I will have no rear wiper and the rear fog lights will be on permanently.

If this is correct and remedies 80% of the problems I can bodge 2 new circuits for the rear fogs and rear wiper, I can't really justify spending best part of £300 on a new AMR5360, I could get a 2nd hand one but who knows whether it'll last..........

Watch this space for an up date

£300 ?!?!?!? ouch!

ebay item 252024018399 is in peterborough, and has a 30 day warranty .... ?

What about the resident electronics guru on here @Rick-the-Pick ? I know he might be more involved in RR electronics, but might be worth an ask

Might be worth a new thread to see if AMR1280 is compatible with the V8 - would hate to think of you causing more problems for yourself.....

( did you check the wiring going to the rear door for a short ?? )

You will require AMR5360 that's for D1s from VA 534104 the electrical wiring is different from the earlier ones due the the factory fitted electrical kit that may have been fitted at the time. One wiring loom and MFU fits all from base to ES models.

AMR1280 is from MA 081992 to the VA 534104 so just for the early D1s.. RRCs also had AMR 1280 so been around a long time.

Compatability of the MFUs has nothing to do with the engine fitted so either petrol ot diesel will do.

discool said:

You will require AMR5360 that's for D1s from VA 534104 the electrical wiring is different from the earlier ones due the the factory fitted electrical kit that may have been fitted at the time. One wiring loom and MFU fits all from base to ES models.

AMR1280 is from MA 081992 to the VA 534104 so just for the early D1s.. RRCs also had AMR 1280 so been around a long time.

Compatability of the MFUs has nothing to do with the engine fitted so either petrol ot diesel will do.

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Have you any knowledge / experience of fixing them at all ? (£300 does a fair bit of fixing .....)

I've opened the box on mine, but can't see any obvious faults with it

Disco1BFG said:

Have you any knowledge / experience of fixing them at all ? (£300 does a fair bit of fixing .....)

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Just the once for my one, took me around 30mins. The photo showing the inside is mine. https://www.landyzone.co.uk/land-rover/multi-function-unit.64509/

Yes £300 plus p & p now http://www.rimmerbros.co.uk/Item--i-AMR5360

Jasonmichael said:

I've opened the box on mine, but can't see any obvious faults with it

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With all thes flow soldered components I don't see how it's repairable.
PCBs are repaired by replacement these days.

discool said:

With all thes flow soldered components I don't see how it's repairable.
PCBs are repaired by replacement these days.
View attachment 98991

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anything is repairable, with enough time and money. The q is whether it is cost effective.

The Mad Hat Man said:

anything is repairable, with enough time and money. The q is whether it is cost effective.

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I haven't seen a PCB repaired for at last 30years plus, replace it, if still available and if not a new updated unit is fitted.

As for the MFU try and find a circuit diagram, component list and its operating protocol then we are talking.

discool said:

I haven't seen a PCB repaired for at last 30years plus, replace it, if still available and if not a new updated unit is fitted.

As for the MFU try and find a circuit diagram, component list and its operating protocol then we are talking.

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Co I work for does it only daily basis - not cheap tho.

I've been all over mine with a magnifying glass, can't see any dry solder or any overheated components / breaks in the lines..........
Looks like i'll be biting the bullet

I am, for the sake of research gonna put a black one in, just to test and see 'IF' there are any compromises