Hi Team I have one of the 1:00 am security alarm problems that seems to crop up for a lot of us old Magna drivers.
The doors will not lock on TH Magna (series 3) Advance by remote or manual locking. When I use the key on the drivers side door to manually lock the door(s) I hear the locking mechanism close then immediately open. The indicator lights flash twice. The security system dash light illuminates. When I use the remote I hear the same actions.
When I sit inside the car and lock the doors internally from the drivers side door only the drivers side door will lock. The other doors can be locked internally by hand.
Also I have had a quick check of the bonnet, boot and door switches but can not see anything physically wrong with them. The dash light indicator for doors being ajar is not illuminated. I have had a brief read of the MMAL workshop manual but can not get near an answer to the problem. Also checked out the forums here.
Can anyone please help me beat the security system problem as it will not allow me to lock the car. 1) Is there a short term solution? Maybe pull out a fuse? 2) How do I fix this problem long term?

A common problem.

It is the switch inside the driver's door.
The solenoids move the door locks, but the switch doesn't register it as completing successfully so the BEM reverses the process. Does the same if everything os working ok but you haven't closed a door properly.

You can identify the correct fuse and remove that, then all doors need to be locked manually and the key will only open the driver's door. The remote will no longer work.
Long term, you need to dive into the innards of the driver's door, and look for bent rods that don't allow full travel, or dismantle the door lock mechanism and clean/bend the contacts to make a better connection.

I bought a TL from a car yard with the fuse missing. When I replaced it, the door locks would do as you describe. So much for a car yard fixing little problems before sale. lol

Thanks MadMax.
I will give it a go