Ok, I would like to draw similarities between the trunk light and the dome light.
From the circuit diagrams, it appears that when in full auto mode, botht eh dome light and trunk lights are turned on whenever any door/trunk is opened. This signal comes from the N10-3 CCM, which detects the open latch via the A37 PSE.
My PSE does not "exist" on teh bus, so cannot send these signals.
Hence my dome light works on the unlock command (which passes via the CCM to the PSE), but does not work when I open the door. (The door pin-switches are OK, since the clocks light and the alarm fires)
So my trunk light does not work on the unlock (no need) and I cannot link via the reading light switch (post-facelift function?), and is not driven by the trunk opening since the PSE cannot report it via the canbus to the CCM. Trunk switch works OK (fires alarm).
Open trunk, and check for light (Process entry!)
Check if trunk light is getting 12V (Might just be a holder problem)
Check trunk light bulb is good using meter or battery to test it lights. (Might just be a bulb problem)
Lock and alarm car. Unlock trunk with key, and confirm alarm fires when trunk is opened. (Shows trunk signal reaches PSE)
Reset alarm, and unlock car with remote (shows CCM talks to PSE over canbus)
Wait for dome light to go out, then open door. Dome light should re-light. (Shows PSE is talking to CCM)
We're now down to the circuitry within the CCM, and the wires leading to the bulb holder. Next stage is to find the pins coming out of the CCM to drive the trunk lamp. (TBD