928 S4 1989 drivers door problem
 

hi everyone this is my first post for my new car which i've just picked up. :bigbye:
as you can expect i have a list of issues but need to start with this door lock issue.

so starts my project. :D

first off i have to sort out the drivers lock. The passengers door lock opens and closes with the key but the drivers does not. if i put the key in the drivers lock and try to turn it left or right it does not move. I'm thinking maybe it is an alarm /low battery issue (which i still have to check) or could it be the barrel or door motor.
the problem now is i can set the alarm but the drivers door will not lock. so if i open the door the alarm goes off. i then try to disable the alarm from the remote key fob where the alarm light then changes from flashing red to solid red, put the key in the ignition but it will not turn over as it is disabled.
the drivers door latch i have tried to manually push down but it will not move.
does anyone have any idea what is wrong or what i should start with to try to diagnose this? is it an alarm or door lock issue. any threads already open regarding this? pictures of fixes? help please

Try if the lock works from inside the car: the akward to reach round turning knob (not sure what Porsche was thinking there) and the electric lock button on the console (above the radio, the red button with a key on it).

First problem: Aftermarket alarm system. These are often troublesome on the 928. Very few installers are capable of correctly integrating the aftermarket alarm into the factory system.

Aryan had some good suggestions. You need to see if the problem is a changed driver's door lock, so the key no longer fits, of if the lock mechanism is maladjusted or damaged so that it no longer will turn.

Use the round knob (the door must be closed before the lock will function) to see if the lock will move at all. If not, try loosening (unscrewing) the round plate behind the know slightly. If that doesn't help, do a search on here for info on removing the door panel. If the round knob will lock/unlock the door, see if the power lock (red button) will also function properly. If the power lock works, the problem may be a changed or damaged lock.