breech:
I'm having a fun time with the same type of problem.
Have found several burnt or over heated wires.
About ready to buy new wiring.
Gone thru the same things you have so far, no results.
Was told that some after market radios being connected wrong with the memory wire can cause problems.
Redid my radio just in case, no good.
Would appreciate it if you find anything to let me know, and I will do the same.
