Burnt some Spaghetti!

Position B: B1-18 Bk B is Back Up lamp circuit. (from page 6 of the Master Tech booklet, 324.pdf) Big clue!
Lucky for you we've been to the rodeo before.

On the interior, the terminal serves as a junction for D1 to B1.
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B1 on the interior is White!
D1 is the black wire to the turn signal flasher unit
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This gets confusing to follow and so is worth redrawing - at least for me.
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It would be worth looking at the thread linked at the beginning of this post to see the connections and at least in his case, the short to ground.
The multimeter readings showed where to look. it took another page or so before he looked there. Last page has the photos.
https://www.forabodiesonly.com/mopa...t-working-blowing-fuse.508597/post-1973745774