I have had my first 67 catch fire due to poor alternator wiring. I have been told that steering columns are the main cause of Mustang fires because there is a constant supply of power and it is a moving part. I also was told that most shorts occur because when turn signal switches are replaced. There is plastic sleeve that goes over the wires where the wires exit the column is never reused and over time those wires will eventually rub bare and can cause a fire.