hi chaps ive got a 1990 classic
whereabouts is the central locking brain control unit ?
i never had any probs but recently i have just changed 3 of my doors
the wiring loom was different on new doors so i changed it and used mine
and now sometimes it is playing up

On mine its under the dash just to the right of the steering column,if you take off the lower dash trim (above pedals) you should find it along with various other relays.