1991 300SL

There are a number of yellow vacuum lines at the door lock vacuum pump. There is also a larger clear/opaque line. The yellow lines exhibit no leak. The clear/opaque has a leak. I can pull no vacuum on it. What does it lead to?

Secondly, the pump only clicks lightly when I actuate the remote. What feeds the power to the pump? Does it come from a fuse someplace? Some sort of other controller? What is the source of the main power for the vacuum pump? Anybody? Help? I am assuming the various lock switches only actuate a control voltage that actuates a relay in the pump - true?

I am hoping to find the leak in the clear-line circuit, and then find a blown fuse as a result of that leak. Please make my day!
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Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport

I've got a '92 300SE, which isn't the same chassis as yours. However, knowing how German engineers like to stick with a theme, I'll bet the line in question is for manifold vacuum assist and it probably runs forward in the car.

On my car, that line wouldn't hold vaccuum either, and while the car was running, or when the key was in the ignition after running, the pump would cycle constantly.

I used ALL-DataDIY to diagnose the problem - if you don't have a membership, I HIGHLY recommend it - $19.95/year for each car model.

Anyway - my line ran forward to a plastic manifold device that feeds vaccuum to several places - A/C, transmission, etc. That $47 manifold was the source of the leak. Replacing that part solved that leak. Curious that it wouldn't hold vaccuum, as it has no moving parts and was in typical German fashion designed and assembled like the proverbial Sherman Tank. I took my old one apart and could find no issues, with vaccuum it doesn't take much of a leak to cause a big problem.

If you know that the line doesn't hold vaccuum, then you also likely know that you should not necessarily assume that what the hose connects to is what leaks - always remember to test the hose itself, plus plug the hose back into the pump and test from the other end to check the valves in the pump.

As for the signal to the pump, I'm afraid I don't know the answer there, but I seem to remember that the design of that signaling system was changed with the release of the new W140 chassis.

Before you worry about that part of the system I'd find and repair the leak in the clear-line circuit and then pull the power to the pump for about 30 seconds. On my pump, certain systems will be taken permanently "off line" if they exhibit excessive demand for air or vaccuum on a repeated basis. I don't know if the 129 pump has this feature, but pulling the power resets the memory for the off line systems.

Hope this helps.