Having seen the spate of recent threads/postings about door latches that might be faulty, and questions of how to test them, I have put together the attached document for a concise list of tests, and expected outcomes which is suitable for all P38 FRONT door latches. I have posted up a version of this in various threads, but have updated the document to be a bit more 'user friendly' to those not so savvy with electrics/wiring and figured I would put it all in one main thread for reference.
I haven't included the rear door latches, as they seem to give a lot less trouble than the front ones, and don't really contribute to the inputs to the central locking system, other than to tell if a door is open.
All of this information is from the RAVE manual, specifically the Electrical Troubleshooting Manual, which defines all of the wiring colours. It is also put together from my personal 'real world' experience of looking at door latches/locking problems and from rebuilding the latches themselves.
Whilst RAVE gives the wiring colours of the loom in the vehicle, it doesn't give the colours of the wired in the loom that comes from the latch on the models post 1996ish. RAVE also doesn't give a logic/truth table about which switch should be in which state when certain operations are carried out, so hopefully this will help give a set of tests and 'expected' results to help owners diagnose whether their latch is functioning properly, intermittently, or just not at all.
To do these tests you need to take the door card off, and need a multimeter set to the lowest 'ohms' setting (I prefer a multimeter with a beep tone function for continuity testing). Also a set of test leads with crocodile clips on either end can be useful for clipping meter probes to connector pins whilst you are performing the tests. Sometimes a helpful assistant can be useful too..
If you find any errors, or parts that could do with clarification, then please let me know and I shall update this reference where necessary.
P38 Door Latch Tests.pdf