Front passenger door lock actuator in the 83 300SD started leaking.
This vacuum actuator has one vacuum connection. The electric vacuum pump
in the trunk pressurizes and vacuums to lock and unlock.

I took a 1981 300D door actuator, which has two vacuum connections
(one for vaccum to pull it locked, one for vacuum to pull it unlocked),
and connected my single vacuum line to the bottom connection.

It worked !

My W126 300SD now has working locks again.

Now, you all probably knew this already, but I am still learning.

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80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250

Ah yes, I see how it'd work, its because the electric pump in the SD pressurizes the locks to lift them and uses vacuum to close them....only one tube. technically then it should work with the single line attached to either port on the lock acutator.......bottom is probably better though...

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)