problem,central locking will unlock from door key once then I have to unplug the pump and plug it back in again and it works again once only.Thanks for help in advance.Wazza.

I don't know if this will help at all, but since the system is vacuum operated it need help. i have heard that once you shut the car off there is only enough vacuum to operate the central locking system 7-9 times. After that you would have to restart the car. Maybe you have a small leak somewhere or your pump is vacuum starting to fail and not creating as much or as strong a vacuum as you need

The ability to lock and unlock only some number of times is only a factor on cars using the engine for vacuum and the engine is not running. The 126 chassis uses a vacuum pump and should lock and unlock till the battery runs dead.

The pump is designed to shut off after a certain pressure or vacuum is achieved each cycle. If the system has a leak and the pressures aren't achievable then the pump shuts off after some time period. I suspect something along this line to be your problem. To test locate the pump in the spare tire and watch what happens. Does the pump shut-off after similar intervals both locking and unlocking? If the time is long try removing the line and plugging it and see the time length.

126 central locking
 

Thanks for help Steve,central locking pump cycles ok on lock[ie positive pressure]but time cycles out on unlock[ie vacuum side].As there is only one line in and out how do I test the system to find problem?.I pulled off the drivers side door lining but the keylock only has wires to it but no vacuum/pressure tube although there is a short pipe at the base of the(blue colour)lock.Thanks again Wazza.