Stuffed Central Locking

Hi

Just bought myself a Charcoal grey 91 svx (Nov '91 even Subaru didn't believe it was '91 till it came up on there computer) The cars great except for one annoying problem. Everytime you exceed 15kph the doors lock which is fine but then they instantly unlock themselves. This happens everytime you slow down and speed up and so frustrating in rush hour traffic. Don't even know where to start looking at the wiring/motors for a solution. Any advise would be great.

Thanks

John

91 Charcoal SVX
93 Twin Turbo Mitsubishi Galant VR4 (Written Off)
89 Subaru Legacy Vi