So I have 2 WS500\'s with Ptype harnesses I used with Balmar 621 alternators on my old boat, moving to a new boat and looking at different alternator options and having issues trying to get p type so wanted to know if it was possible to convert the harness from p type to N type
Yes it is possible but Wakespeed does not share this information freely as they say incorrect configuration can cause serious damage. If you contact them directly they may be able to help.
You will probably find that is more easy convert the alternator insted.
From negative regulated alternator over to positive.
I agree with Trond Arvid.
I prefer also to have p=type regulated alternator.
I see more advantage for this, for different other reasons also.
Most off the time easy to modify the alternator.
Both Trond and Ben make a very good point. To switch an alternator is usually as easy as finding the brush wire that goes to the diode bridge and moving it to ground instead. Your other brush then becomes your + field wire.