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I bridged the circuit board directly to the head from the b/r switch terminals and it still wouldn't turn on.
Ok. So, the problem is (1) the yellow wire, where it goes into (2) the place where it connects to the yolk wiring harness.I was able to identify the problem by gently pulling on the wire where it went into the gromet at point 2, where it easily detached. (Attachment Link) It's manufacturer's part number is 907280-02 and is referred to as the "PCB to yoke loom"
This loom is the usual suspect.