HA, that radio is worth like $1 on the street.
No harness plug needed. Cut that crap off. I did on my boat, it was loose and corroded that could lead to crappy audio. The wires are standard stereo colors (front LR rear LR power, ground, key, dim). Just use some standard heat shrink style crimp connectors. Done and done. The radio will still have it's plug if you ever need to remove it.

I had a Kenwood marine KMR-350u in my H180. Sounded amazing and around $100! Way better then the JVC-KDX50BT I installed in my new boat. Kinda wish I just purchased it again, but it doesn't have bluetooth (and not wet rated but it wasn't a concern on the cuddy). The kenwood has water sensors so when it gets splashed it shuts down to protect itself until it's dry.