Disco 1 Interior Light door switch wiring

StuRox · Nov 8, 2024

Hi All,

Trying to solve an issue with my sons 1995 300 TDi.

Interior light comes on when you manually switch the switch on the dome light, but will not come on when you open the door.

Have changed the MFU with a unit that has been tested.

Have tested my sons dome light in my 1996 300 TDi and it works.

So I now investigating all of the door pin switches, but my question is, where do all of the door pin wires end up, as I thought I would also check the whole wiring to make sure there are no breaks in the wires going to the door?

Also, his rear demister switch seems to not work either - no click from the fuse box relay as if it is trying to switch it, so maybe thinking dodgy switch? But anything else to check whilst I have the voltmeter out?

Any help appreciated.

Cheers

sierrafery · Nov 8, 2024

Hi, the door switch inputs are going into the MFU, you should get earth when you open the driver's door on the PG wire pin 18 of MFU's plug(C205) for the lamp to come on... if you get that input when you open the door and the lamps are still not coming on you must check if that earth is coming out ffrom MFU's pin 1 and if it does the problem is between that point and the lamps relevant parts attached but you can go deeper in this https://smallpdf.com/file#s=28eecf7a-e01e-411e-a246-ad6bafa89734

StuRox · Nov 8, 2024

Perfect, will give me more to check this weekend

discool · Nov 8, 2024

As you say “Have changed the MFU with a unit that has been tested” I take it all the other circuits controlled by the MFU were ok when the diagnostic test was done.

As the heated rear screen relay is also switched by the MFU and which requires the engine running when checking the rear heated screen relay is functioning, the same with the front heated screen.

It’s the MFU that switches on the interior lamps via the door pin earthing, so its strange its not doing that when any of the doors are opened, does unlocking with the fob still illuminated the lamps.
Finally is this issue why the MFU was replaced ?

Stanleysteamer · Nov 8, 2024

sierrafery said:
Hi, the door switch inputs are going into the MFU, you should get earth when you open the driver's door on the PG wire pin 18 of MFU's plug(C205) for the lamp to come on... if you get that input when you open the door and the lamps are still not coming on you must check if that earth is coming out ffrom MFU's pin 1 and if it does the problem is between that point and the lamps relevant parts attached but you can go deeper in this https://smallpdf.com/file#s=28eecf7a-e01e-411e-a246-ad6bafa89734

Without wishing in any way to hijack the thread, could this be the same on a D2? As mine does exactly this.
If not, I'll just leave it cos I can live with it.

sierrafery · Nov 8, 2024

Stanleysteamer said:
could this be the same on a D2?

no, here's about D2 https://www.landyzone.co.uk/land-rover/interior-lights.379040/#post-5357685

Stanleysteamer · Nov 8, 2024

sierrafery said:
no, here's about D2 https://www.landyzone.co.uk/land-rover/interior-lights.379040/#post-5357685

Thanks M8!

StuRox · Nov 8, 2024

Changed the switch to mine and rear demister now works....so new switch is on order and that's sorted.

His fob stopped working ages ago and fitted a new central locking unit (non Land Rover) so that's not really helpful on diagnosis, but doesn't light when you open the door.

Will check all the earths this weekend and go from there. I only changed the MFU as it all pointed to that being defective....ha hummm Land Rovers eh.....

StuRox · Nov 10, 2024

After all that, his MFU was fine and the negative earth from the EMF was not reaching the interior light,.so guessing issue with alarm module as his one button fob stopped working. Ran a wire direct from the MFU to his switched earth on the interior light and all is good.

Disco 1 Interior Light door switch wiring

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