That's the beauty of it
Since the charger has a terminal block, you undo the old leads (120vac input and 12vdc output) and connect them up to the new one. You will need to run a separate ground wire to the bus bar behind your power panel and the included wire with the RF-11 (?) and terminal lug (that I understand is a thermistor).
BTW, my ProNautic looks nearly identical to the Sterling in the picture.
On my 310 I needed to splice in 5' of wire. There are only two wires inside the wire and I just happened to have some similar wire on the boat. Pays to be a pack rat sometimes.
Ran the temperature sense wire on the port side under the rear bunk. Note there is an extra 1" tube outboard of the tube where the wires from the battery charger are run that goes under the head. Pretty simple.