Simon,
I cannot answer your question, but I think that the sense wire should probably be connected to your house battery and not engine battery We fitted a Sterling Alternator to Battery charger, so no sense wire needed now, but one was fitted when we got the D34P in 2012 92005 boat) Sorry I cannot be more helpful at the moment, presumably the alternator is charging your batteries at a reasonable voltage and current, perhaps about 14.2 volts assuming open cell lead acid, or a bit less for sealed. If I come across any more info, I shall post.
Angus
The membership association for owners of Dufour Yachts