Pictures of wiring please

That is REALLY some nasty looking stuff. What are the two wires hooked to the "push on" terminals on the starter relay? One looks? like it's got yellow tape all over it?

In the bottom of your photo is a big red wire spliced to "something else" with a blue connector. That connector is known as a 3M (brand) "Scotchlok" and those are pieces of **** from the word go.

What color is the "mystery wire" black? with ?? tracer? says 'here is the other picture'

That APPEARS to be one of the two that connects to the starter relay, should be black / yellow tracer?

What do you mean "middle block far left," you talking about the top left of the bulkhead connector?

LOOK at your wiring diagram. LOOK at the wire color. Have you downloaded the 66 shop manual?

Page 306 that is 8-118. I'm not sure what cavity you are referring to. It might b D? Violet? would be part of the back up lights harness for a stick transmission. Automatic backup switch is in the car, on the shifter linkage