I purchased a rust free, low mileage 1991 Mustang 5.0 convertible, which had serious electrical problems. Most of the under dash and engine compartment wiring was messed up. The sons of the prior owner wanted to upgrade the sound system. I've spoken with several people about repair or replacement and no two answers were the same. One expert told me all 1986 to 1993 harnesses are interchangeable. He sold me a harness from a 1989 coupe, however, it was marked 1988 and did not work. Some wires plugged in and others didn't. I was later told that the 1988 harness takes considerable modification. I've been advised to buy a complete parts car, preferably a 1991 5.0 and strip the wiring. Can anyone give me some direction?