I didn't note the date on your 300SD, which is indeed a W116. I'm not sure if the systems are separate on that series. On mine, a W126, there were (4) 3-ways and the (6)end pieces I picked up at Pep Boys I believe. Yours may be different and I don't want to steer you wrong. I just poked my head under the hood and counted them. Fastlane carries the 3-ways.

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Sam

84 300SD 350K+ miles ( Blue Belle )