83 sd door locks
 

I am trying to figure out the door locks in my 1983 300sd. Sometimes when I lock the driver door with the key they work fine. Sometimes they cycle through twice-ie. they lock then open then lock again. Is this a problem with the pump in the trunk or possibly the switch in the door? The key feels a little tight. It might be contacting the door switch for too long?

Thanks,
Paul

I would suspect the problem is in the trunk. The schematic shows a Sequence Pressure Switch in the Supply Pump Assembly that changes the sequence from vacuum to pressure. But then again, a slight leak anywhere in the system might cause the system to not hold enough pressure to completely make the sequence switch. But the best place, and what fixed mine, is the flex line at the pump assembly. With such an intermittent problem, it would be tough to isolate until it fails but a mighty vac might show a very small leak.

Read this thread. I think every one with a 300sd has had door lock problems at some point and there are a lot of threads about it

http://www.peachparts.com/shopforum/diesel-discussion/176562-ok-i-am-going-fix-my-door-locks-where-start-2.html