Light stay on
 

The lights will not go off, despite being switched off. Ocassionally they do go off, then come on later when the car has not been touched. As soon as the ignition is turned on, the head lights come on as well as the side lights; the head lights only go off the normal time delay after the key is removed. however, the side and tail lights stay on.

Two questions - likely fault and whether a complete replacement of the light switch unit is required.
And - which fuse should I temporarily remove to stop the discharge of the battery?

A replacement LSM is the cure. the temporary fix is to unplug the LSM ;)

You could remove both fuse link 9 and 11 in the engine compartment fusebox, or simply disconnect the battery earth lead.

Brian :D

Thanks Brian.
The problem seems intermittant. The lights go off after several hours, then come on again for no reason. I might add the car is not currently being used.

I won't disconnect the battery lead as the car is then immobile, but disconnecting the two fuse links might be an option if the solar powered battery charger can't keep up.

I'll be taking it for mot in a couple of weeks but don't know if it will fail if the lights won't go off - it's impossible to turn off the headlights when the ignition is on.

So I'll be looking for a LSM (light switch module?) unless a repair is possible. As it's an intermittant problem I wonder if it's worth opening up the unit to investigate - bit of dust or insect in there perhaps?

Big russ is your nearest helper, failing that you are probably the same distance between Brian and myself!

Lsm's have to be virginised before use, you cant just swap it out for a used one.

Check the battery voltage when it happens, the headlights and tail lights are switched on by default if the battery voltage falls too low (about 8 volts from memory).

Really? How weird. Why? Can anyone confirm this?

Does this mean that on my other stored 75 the lights will have come on as the battery loses voltage due to the alarm, then eventually go off before the battery voltage eventually falls to zero.

Will cars parked longterm at airport car parks also be confusing attendants there by lighting up unexpectedly?

Incidently, I don't think battery voltage is an issue with my car as there is enough juice in it to start the engine.

I guess I'll need to see you or Russ for this. Perhaps I should ask you for an LSM from the next one you break (along with the hi-line satnav harness I mentioned)

PS Love the term 'viginised', is it in the OED yet?

In that case, it may not be your problem.

The low voltage only switches the lights on when the ignition is also switched on, so will not affect cars that are parked up.

How strange, especially when you want all the voltage there is to start the engine.
I'd be very surprised if many owners knew of this feature, and wonder why it was included in the design. Is it mentioned in any handbook or manual?

I don't know if it is any manual, it is a sort of emergency setting, several electrical items are inhibited when the voltage is too low, but the lights are switched on.

There is often a query about the headlights 'flashing' when trying to start the engine with a low battery.
What happens when trying to start the engine, there is not enough power to operate the starter motor, but it pulls down the voltage - enough to switch the headlights on - and then the starter solenoid drops out, disconnecting the motor so the voltage rises - enough to switch the lights off and operate the starter solenoid again, which connects the motor, which pulls down the voltage........... and the cycle repeats, with the lights being switched on and off, as long as the ignition switch is in the start position.