So, fitting the new interior light has led to a new problem, in that it seems my alarm and immobiliser might not be working. Here’s what I know...

1) Door switches are all good, removed them and tested.
2) No lights come on when I unlock the car - I know the lights go through the AC10 before being grounded to doors?
3) when I lock the car, the little blue LED on top of the dials flashes.
4) if I lock the car with me in, I can move about (suggests the motion sensors aren’t activated?)
5) if I lock the car with the central locking buttons I can still start it - if the central locking fob is on the passenger seat it still starts.

So... any ideas? I was going to take a check of the two fuses in the fuse box this morning - I think they are anti theft alarm - ECU/BBUS, and the Alarm relay fuse? Could it be something as simple as the alarm relay? Is there a simple way of testing that?

Thanks will let you know how I get on. I was basically going to work my way through the wiring diagram until I got to a component I couldn’t prove was working but I suspect it will be something like the AC10 in which case I won’t have a clue haha

Should have said, it’s an aftermarket system I believe........

try https://www.lrworkshop.com/electrics/defender-2002my/anti-theft-alarm-and-central-door-locking-cdl