Interior light help please

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towsey956

towsey956

Well-Known Member
Posts
1,104
Location
Northyorkshire
Hi all

I've looked in the search bar but as usual can't find anything useful, me and that thing don't get on.

Opened the door on my 98my 300 disco today and noticed that the interior light was flashing irratically, thought plunger was dodgy but no it's ok. Tried all the doors and the same thing happens, but then sometimes it's fine for a while, and it works fine when I switch it to perminantly on. could it be the box under the dash?

Cheers

Towsey
 
It could be "the box under the dash" the multifunction unit, as that controls the interior lights so why not put the unit into its diagnostic function to test it. Are all three lights are flashing at the same time, do have led bulbs?
 
Cheers for reply

How do I do the diagnostic check on it please? Yes all lights flash at same time, and no their just standard

Many thanks

Towsey
 
Hi Mate this happened to me, I tried all sorts but worked out to be a faulty bulb and the holder was damp so changed both and perfect, worth a try
 
Cheers peeps

I did try searching for this but could only get 2 replies and neither were wot I needed, I did find wot you had written on another forum tho saying the same thing...I really don't know how people manage to find stuff in the search bar

So if I do the test and the lights flicker for the 2 seconds it applies power, does that tell me that the unit is dodgy or that the unit is putting power out but something else is dodgy? And if it's having an OK moment, will it tell me anything?

Thank you

Towsey
 
Looking at RAVE, It looks like there are two different wires from the door switches going to the MFU and the Theft Alarm Unit.
It's difficult to work out exactly what's going on in the MFU, but from the limited information on the drawings, it looks like the interior lights are driven by a transistor rather than a relay switch. It's worth noting that because a relay circuit is much more likely to give a flickering lamp when they get old and/or dirty. An electronic switch is extremely unlikely to give a flickering on voltage.
However flickering can be the result of dirty or insecure pins and sockets in the connection systems, although it could also be the result of an intermittent (or dry) joint inside the MFU, which could mean having to check the MFU with a hot soldering iron and a magnifying glass.
As I've already said, the door switches present two inputs to the MFU, one from the driver's door and the other from the other doors, the tailgate has a slightly different input but reaches the MFU by the connection for the other doors. This splitting of the inputs is probably to do with the Theft Alarm Unit. If the lights are flickering irespective of which door is open then I think it's fair to say that the fault is not on the input circuits to the MFU but probably on the output wiring from it.
The Purple/Blue coloured wire from pin 1 of connector C205 on the MFU might be a good place to start, but be prepared to check or get the MFU checked out. It's unlikely that the self test diagnostic routine will tell you anything you don't already know.
c205.gif
 
The MFU test is purely a function test of the output circuits it controls, u may find one of the other circuits not functioning and so giving an indicatation the MFU is possibly on is way out, if that's the case it's not surprising for electronic kit which is powered up 24/7, yours could be on borrowed time as it could be 18 or so years old.
My MFU failed compleatly when the vehicles was 14 years old.
Does the ignition switch illumination also flicker?
 
So after you have found the Purple/Blue wire in the MFU connector just extended it with a piece of wire to an earth and the interior lights should illuminate.

But firstly u must undo the two screws retaining the fuse board, unplug one or two wires that lay across the front and turn the board around, only as far as needed, to get access to the unit on the rear, then while holding the fuse board steady pull to unplug the connector from the unit after pressing the locking tabs.
The MFU is also plugged into the fuse board so there's a multi pin connection below the unit.

The two hex crews are a pain at remove/replace, I found I had a speed race the exact size, how come I had that in the toolbox I will never know, but a 1/4 drive socket with an extension will work.
 
Thanks for all that, I will spend some time with her when I get chance. I unplugged the ignition light cos it also does the stupid bonger I was sick of hearing, but it still bongs when I open the door and the lights are on which is fine

Thanks again

Towsey
 
towsey956 said:
Ok people...so why won't my disco do the diagnostic test???

Towsey
Click to expand...
The start procedure hasn't been followed or there's a fault somewhere, I think that's it, as the start is simple the test should start straight away, it's quite spooky when things start happening on their own.

Have u manually check the function of the items that are on the list, like wiper delay, rear fog lights, etc etc. Although the interior lights illuminated and then flash do they still have the time-out delay.
 
Haha I don't mean to be

The instructions I found for doing the test start with holding the heated rear window switch in whilst turning on the ignition, then letting go of it within 2 seconds...

Yes everything on the vehicle works as it should

Towsey
 
What's next I don't know, there has previously been post on not being able to access the MFU diagnostic but they also had other issues with one of two of the circuits it looks after.
So back to old school basics, check the electrical connections are in place and clean, plus as stated already with the Purple/Blue wire at the connector extended it with a piece of wire to an earth... the interior lights should illuminate.
I don't think it will go anywhere, but u may have an iffy bulb or bulb connection that causes the MFU to mis behave..
 
I have the same the same problem with mine, flickering interior light, which now stays on constantly no matter what I do, other than pull the bulbs. Tried all the tests I could, replaced all the door plungers, checked all the wiring connectors & bulbs, even got a second MFU, still didn't work. Got to the end of my tether with it & reluctantly got a spark to look at it. He spent ages testing the circuits, wiring, MFU and other stuff.

This is going back about 6 months, so bear with me........

He finally narrowed it down to the alarm ECU and stated it was faulty. I can't remember what it was now without looking at my notes I made at the time (which are still in the garage) but it was something to do with the signal from the alarm box to turn off the interior lights when doors are opened & then closed pins 5 & 16 Grey connector. He did manage to show me what should happen and made the lights go out (as they should) but he said its sommat on the circuit board thats knackered.

He gave me the option of trying to find a new 2nd hand alarm ECU & get it coded or he'd rip out the old unit & fit a new one.

Sorry I can't be more helpful at the mo as I knackered my back in (3 lumber discs :oops::oops::oops: ) and haven't touched or looked at it since, its gathering rust, I mean dust in the garage:(:(:(:(
 
Cheers for your input mate and you have my sympathy, my mum did Sumat similar a few years ago.

I have a mate who is an auto electrician but he gets serious quickly...he likes taking dashboards out haha, good bloke tho and I'm sure he'll help if I ask him. Il have to have a good root about when I get chance

Thanks

Towsey
 
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