To remove the lower dash panel, you need to:
1) remove a couple of screws (5 or 6),
2) remove the grating in front of the lower ventilation duct (90 degree counter clockwise turn of the plastic bolt before taking out; the rear part is just hooked in the heater housing)
3) remove a plastic clamp near the accelerator pedal
4) unscrew the hood release, pull it out of the lower dash panel a little, pull the outer cable out of the release to be able to rotate and pull the inner cable out of the release (not an actual pain though)
5) remove the panel while watching out for the parking brake release (the side of the panel is hooked in the side of the dash; push panel downwards to release)
The A pillar panel is clamped to the A pillar with three steel clamps. After removing the door entrance velvet-like trim along the A pillar, you can see the clamps. Push the A pillar panel towards the inner side of the car starting at the lowest clamp (you can use a screwdriver to push gently at the back of the actual clamp). Work your way up and hook the top of the A pillar panel out of the ceiling headliner (push the pillar down, twisting it over the dash).
After you have removed the A pillar panel you will see some wires that are hooked up the A pillar and you can add the detector wire along these.
The rear view mirror has to be pulled off before you can take out the courtesy light. The mirror is clamped in a bracket and has to be pulled down (this can be quiet a hassle). If you have a rear view mirror with the remote control receiver or auto dimming function, you have to beware not to break the mirror housing or wires when pulling the mirror off (always pull the foot of the mirror and not the mirror itself).
After the mirror is removed, you can easily remove the courtesy light.
good luck & greetingz,
with a minor 600+k