Default setting seems to be to keep the boot/petrol cap locked when central locking stops working - i.e. opening drivers door with key does not unlockboot/petrol cap
Followed advice on a jaguar Forum regarding problems with central locking on a 1992 XJ40 - replaced central locking unit - located under passenger glove box - success - now working.
However - I found that wiping the terminals on the old unit with 400 grade sandpaper also fixed the problem
THE UNIT WAS NOT FAULTY - JUST HAD DIRTY TERMINALS !
Conclusion - Dirty earth (black wire) terminal may have been main culprit for non working central locking on car

 

Welcome to the forum johnboyce,

I've moved your thread from General Tech Help to XJ40 forum. This is the place for technical posts about your model.

Please follow this link New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum to the New Member Area - Intro a MUST forum and post some information about yourself and your vehicle for all members to see. In return you'll get a proper welcome and some useful advice about posting to the forum.

Graham