Interior lights not switching off

[YMGF1]

Having had a comprehensively flattened battery I investigated and found both mirror lights and both foot well permanently on. I tried the different modes of getting them to switch off such as turning ignition on, arming the alarm and simply waiting 9 minutes. (A bit longer actually). None of these caused the lights to switch off.

As the only item in common is the ECU through which the lights are grounded, I unplugged it. Have I got the correct part, shown in image?

What I didn't expect though was that when the ECU was disconnected the lights are still on...........

Presumably there is an earth fault but the wires around the ECU look absolutely fine.
Has anyone had this fault or have any solutions please?

Many thanks
Michael

[ArntyR]

Hi YMGF1. You don't say whether it's both doors or one only. In my F it was passenger-only. I got a 'fix' by squirting the lock area liberally with WD40 and working it in with repeated opening + closing. I anticipated needing to replace the lock mech with a used unit, since the switches are hidden inside it.

I'd guess yours, too, is a feature of one door only and due to a seized/worn/dirty microswitch(s) in the door lock mech, that's behind the door-card.

Imo your attachment looks like a 5AS scu/bcu (security/body control unit) that locks + super-locks a healthy door lock. (Your remotes are squarish Lucas 5AS units?)

ECU is LHS rear of the engine roughly mirroring the coolant reservoir area. (I don't think this operates the door-lights tho')

Hope this helps.

[YMGF1]

Hi ArntyR, thanks for getting back.

Yes, you're right about it being Lucas so I think I've extracted the wrong module! No wonder it didn't make a difference.

I've since learned the correct module is behind the drivers side fuse box. Getting to that will have to wait until next weekend. It confused me as it's not too clear from the manual that it's fixed to the back of the fuse box and can't easily be seen without conducting automotive surgery.

As all lights are permanently on I think it must be this ECU as even if a door is left open the lights should extinguish after 9 minutes.

I'll take the module out next weekend and let you know if i resolve it.

Michael.

[ArntyR]

Yes, it'll be useful info to share.
Loadsa luck with it.

[talkingcars]

The ECU controls the engine.
The 5AS controls the alarm.
The BCU controls the lights, this is behind the fuse box.
However I would start with the drivers door lock.

James

[YMGF1]

Thanks James, I'll have a look this weekend and let you all know how I get on.

[Rob Bell]

If you have access to a pscan, the 5AS can be interrogated for stored errors.

Lights remaining on however is a strange one - I don't know if this is an ECU fault or a short of the switched earth to ground?

[YMGF1]

Thanks for the replies Rob and James. I'd read the description of operation in the electrical manual which says that even with a door open the lights would switch off after nine minutes. With this logic I thought it must indeed be an earth problem, but in hindsight it seems the description is wrong, at least for 2001 vintage.

Exercising the drivers door lock with the key made no difference, but when I disconnected the two plugs in the drivers door normal service was resumed, (albeit without the driver side functioning), so I concluded it must be a fault in the lock mechanism.

I decided to replace with new and this has cured the problem, but I will investigate the old lock at some point.

For anyone contemplating this, it's quite a fiddly job. I found that removing the lock barrel and re-installing it from inside the door before you locate the exterior handle was easier. You can reverse the direction of the barrel retaining spring clip to install it upwards which will also help. (You'll see what I mean when you are doing it).

I also suggest using bluetack on the heads of the two screws which secure the exterior handle to avoid dropping them inside the door.

Michael

[Rob Bell]

How interesting! Thanks for that update Michael. There have been detail changes to the electrical systems on our cars over the years. The lights on my 1995 MGF definitely switch off after a time (I've never actually timed it, seems shorter than 9 minutes though?) Strange that this useful feature was removed for your later 2001 car? I thought the multifunction unit would have been the same?

[YMGF1]

Thought I should post a further update and conclusion. Having replaced the drivers door lock all was fine until last Saturday when I found the battery again flat.
Convinced an earth fault must be to blame I dismantled various parts of the centre console and closing panels to check for chaffing of the loom, all to no avail. Finally I turned to the rear view mirror and removed the horizontal trim panel from the above the windscreen to reveal the wiring to the mirror. That's where the problem lay, with all three wires trapped by the trim and one, (the return), shorted by one of the screws holding the sun visor.
The two strange things are why it's only just appeared as a fault. I did remove that panel but a considerable time go. (This is most likely self inflicted). The other is why the door lock being changed cleared it for a couple of weeks.
Still, having seen the shorted wire I'm confident now this is resolved.

[ArntyR]

YMGF1, I bet you're relieved and it's good to have feedback linked to your problem.

I've had that panel off before w/out realising the screws can damage the wiring, so it's good to have that warning for next time.