WD40 is not an electric parts cleaner. It will leave a very, very nasty film. I love the stuff, but its uses are limited. Might want to pick up some electric parts cleaner.

X63 should be a connector, but no clue where it would be. The dual horn system is annoyingly complex.

Is there not a component location chart with the reference? Most I have seen have those in the back. An actual picture of the car or area with labels for every connector, part, etc. Generally several pages of pics.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car