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What ??

Don't see any of that on my 124.066 lighting schematics..
I see trunk sw S 19/8 and plate lamps E 19/2 and 3 [ R/L] , along with same circuit for High Center Stop E 21 . but no Mercury switching.

The reason I ask to test trunk sw in Off position is to eliminate possible chafing of wire in lid or at harnes/hindge pivot point

I assume you have tried the High/Center??