I'm guessing the third hose went to the heated windshield washer container or the heated windshield. Since the end is now not attached it should leak. Since it must not be leaking I have to assume the other end has already been plugged off. Determining that would determine how I would fix it as there really is no reason to worry about reattaching it if its already by-passed.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician