The locks all work manually, but not automatically.

Sorry for the vague question, but I know nothing of this system on the W124's. Where do I start?

When the lock system on my 300D (W123) went out, it was as simple as reattaching a vacuum line in the engine compartment. But I have been told that these are not the same.

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2004 E320 Wagon W211
2000 CLK430 Convertible W208
1985 300SD W126
1983 300D W123