Can any one tell me where this vacuum line is supposed to go? It was just sitting open when I got the car so I plugged it for now. It had a blue pressure regulator thing on it that I took off to plug it. Thanks for any help. It's on a 76 W115 300D.

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I searched for a diagram for your car and the only thing I could come up with here is a dead end which is several years old.

I think if you'll look around a bit you'll see where that line goes by finding a cap on another line or a pace where it should be plugged into the vac system. Clearly what you've photographed is headed toward the rear of the car or into the cabin.

An indication of the function of that supply line should be obvious from having an entire system down. If the car shuts off when you turn the key I'd suggest the line is not one to your ignition. That of course is only a simple example.


My guess is that one of the previous owners capped the vacuum system where that line attaches and since the system it supplies vac to had failed he didn't worry about the end you capped. He didn't want a bad system effecting the other functions of the vacuum pump.

I am not familiar with any MB which I do not own so I can't guess what that line is supplying vacuum to. My SD uses vacuum to open and close air supply flaps to the heat and AC system, make the transmission shift properly and shut the engine down. There's probably more but that's all I've dealt with so far.

I think the older diesels had the door lock and unlock system running off the vacuum pump located on the engine too.

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84 300SD
85 380SE
83 528e
95 318ic

looks like its in the area for cruise control?

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1981 NA 300D 310k miles