Mike,
When I bought my new Instrument panel from Seaward Products I also purchased a brand new wiring harness (a little extended lenghth) because why not replace all of that 20+ year old wires. I would highly recommend the replacement with new wires. This makes the job easier and gives you the piece of mind that all of that wire is new and should be trouble free. Also, as I recall, some of the old wire colors may be different so it is easier to install all new panels and wiring. Do it right the first time and you will be much happier going forward.
When I bought my new Instrument panel from Seaward Products I also purchased a brand new wiring harness (a little extended lenghth) because why not replace all of that 20+ year old wires. I would highly recommend the replacement with new wires. This makes the job easier and gives you the piece of mind that all of that wire is new and should be trouble free. Also, as I recall, some of the old wire colors may be different so it is easier to install all new panels and wiring. Do it right the first time and you will be much happier going forward.