Yeah, did a search, but still have questions. Does anyone have a hint as to what might be the fault in my 1983 W126 turbodiesel central locking. Symptoms are: trunk pump works for 45 sec. -which shows no or insufficient vacuum pump down. All lock buttons in doors are pushed (pressurized ?) in up position except driver door lock(I'm thinking that this showes the pump is building vacuum). Passenger door does not respond to key operation but driver door does. Trunk lock will respond to key. Fuel lock does nothing. Is there a electric switch in the driver door that controls the switch-over point from locking to unlocking that could be the problem? Something has to control the locks knowing to unlock/lock---where and what is it?

Many thanks,
Regards,

Run-em
1983 300SD--aka--SPARKY THE DIESEL

The 81 SD has a central locking key switch in the driver door only. The 85 SD has a central locking key switch in both front doors and the trunk. Not sure what the 83 SD has. The switch sends a signal to the pump when you set the key in that position. I don't remember if it's a continuous signal or an impulse. If the pump responds in any way to the key switch I'd say the key switch is fine.

When you turn the driver key switch to lock, the pump should run for about 5 seconds to suck all the vacuum pods to locked position. When you turn the driver key switch to unlock, the pump should run for about 5 seconds to push the vacuum pods to unlocked position. All the doors should unlock when you open the driver door from inside.

If you can borrow a known working pump, try that. If not, apply a vacuum to the fitting at the pump and see if that gets the doors to lock. Also check that the system holds a vacuum for at least a minute. Then apply pressure and see if that gets the doors to unlock. This should tell you if the problem is inside the pump or a leak somewhere downstream.

Sixto