So for the last few month I have been having problems with my 99' Lexus IS200. It seems that there was a problem with the alarm that has been setting is off at all hours of the morning. The only way I found around it was to leave my car unlocked over night, which wasn't very comforting. So I was reading around the forums for a fix but I couldn't find a clear solution for it. I found that it may be the motion sensor that was causing the problem but I couldn't find out if it could be disabled or how to disable it, so I went hunting.
I decided that I would remove the roof lining and heat shrink all the wires as this may have been the problem. After pulling my entire roof apart I found that the motion sensor itself was inside the dome light and that it was as simple as unscrewing 3 screws and disconnecting a single harness. So if you are having the same problem try disconnecting it before you go ahead and waste a lot of time haha. I have only just disconnected the sensor so I'm not 100% sure if it is the problem but I'm certain that it is. I will post back in a few days telling you how I go.
Disable motion sensor
Time: 5 minutes
Motion sensor harness:
The big circle is the motion sensor.
The small circle is the harness to disconnect.
Removing roof lining
Time: 40 minutes
1. Remove the A-pillar by gently pulling.
2. Remove the B-pillar by removing the seat belt cover, unbolt the 14mm seat belt bolt and gently pull the cover off.
3. Remove the C-pillar the same as the A-pillar.
4. Remove the map light by pulling down or prying it.
5. Remove dome light by removing the lens cover and unscrewing the 3 screws.
6. Remove rear-view mirror by prying the cover and removing the 2 screws.
7. Remove the sun visors by removing the 2 screws on the outer side, disconnect the harness and remove the screw holding the pivot point.
8. Remove the grab handles by removing the covers on the end of the handles and unbolt the 2 bolts on either end.
9. Remove the 2 push in clips near the rear window(sorry no pictures)
10. Remove the roof lining. The roof lining should now be completely free. The easiest way I found to get it out is by folding down the passengers seat and removing the liner through the rear passengers door.
I hope this helps anyone who is having the same problem as me. If you have an questions feel free to post of pm me.
If anyone is curious I may weigh some of the part for those wondering about weight stripping
If you would like to see more photos click the link below: