Agree with Jim about the fuse. I have heard from many people that the fuse looks good but sometimes has micro faults in them making them to behave abruptly.
Clean both end contacts with an erasure where the fuse fits. Also replace the fuse with a new one .
While at it check all the electrical plugs and connections asp those related to ACC.
My feeling is its loose contact( that also includes corroded fuse contacts and broken fuses). If not it could be the ACC unit itself. I hope its the first one. Good luck.
MVK

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1985 300D Turbo 179,000miles