Why would you think it's that?
Sure, it's possible but with old wires that are tightly tied to each other, it's less likely.
Check the easy stuff before you dig into that kind of thing.
Diagnostics is testing, not getting suggestions and asking more questions after not doing the testing. It would be nice to have a little light that goes on and corresponds to the exact causes but we need to do the work in order to find out why things have failed.