Some of this technical debate is beginning to worry me.
First of all Numan is absolutely correct in everything he has said, anyone who thinks otherwise should get hold of the workshop manual CD and spend quite some time reading!
Please understand that the 147 electrical system is technically completely different to any previous Alfa Romeo and requires a detailled understanding of the system to adequately diagnose and repair it.
Without any knowledge of the skills of the technician concerned I wouldn't speculate on the accuracy of the diagnosis- but even an incompetent technician would replace the bulb first rather than trying to find a complicated electrical problem......!!!!!!!
As for some of the subsequent advice, DO NOT use a screwdriver (tungsten filament) test light for diagnosis of electronic problems- especially if you don't have or understand the wiring diagram.
This is extremely important as the CAN lines are copper wires like the rest of the wiring loom. These important wires carry data (digital signal) around the vehicle- the consequences of causing serious damage by earthing these out with a test light don't bear thinking about.
This is the reason why Numan mentioned use of an oscilloscope, which can pick up the data signals without affecting the integrity of the network.
Please consider that at the very least using incorrect diagnostic equipment and methods will make diagnosis of the ACTUAL PROBLEM much more difficult by causing incorrect faults to be logged within the system.
As a mechanic I entirely sympathise with the technician, it is an unusual problem that probably won't be easy to solve- especially when under pressure. Remember that technicians are simply human beings trying to do an increasingly difficult job- give them some space and understanding and the results will end up better for everyone.