After reading through you question Ive come to the conclusion you've done it all save for one thing and you mentioned it in your statement "wiggling the wiring harness WILL get the car to start" I would replace the wiring harness . One of my pet peeves is when a test light is used to find faults in wiring and a mechanic pokes a hole in the wire which then corrodes inside the plastic and you cant see that its gone bad . Then you get weird things like this happening. you can do continuity tests and get fair results but heat the wires up or move them and it can be a different story . I would replace the wiring harness . it may be a bit more than finding the offending wire and replacing it but speaking from experience you can spend a lot of time searching for that wire and if by chance its more than one wire and you think you found it but it was actually two . Just easier and more certain to replace the whole harness. Hope this helps