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I didn't when I pulled the Blose out of my 85. I strung new speaker wire.
However I have used factory wiring in other cars and it seemed fine.
In fact I just replaced the HU in my wife's PT Cruiser with an upper end Alpine unit and used the harness to connect to the factory speakers, and am shocked with how good it sounds.
With all the rattles and resonance in my 85, a subtle improvement in speaker wire would not even be noticed.
I'd run new wires. While you have it apart it doesn't take that long and at least you know you've got a good product in there. You can get decent Scosche stuff at walmart. Remember, the original stuff has been there for 20 years.