OK, I get it. By switched fuse you are referring to the ignition. I would go through the firewall in that case, too. Sometimes a piece of wire, like the solid copper you can strip out of a piece of Romex, makes a good wire fish getting through those grommets. Sometimes it's easier to fish it backwards, too (engine to interior) Good luck.

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1982 Mercedes-Benz 300CD
1982 Mercedes-Benz 240D - stick