Joined: Aug 2010
Posts: 12,728
Likes: 2,106
From: Madison, WI
Bikes: 1961 Ideor, 1966 Perfekt 3 Speed AB Hub, 1994 Bridgestone MB-6, 2006 Airnimal Joey, 2009 Thorn Sherpa, 2013 Thorn Nomad MkII, 2015 VO Pass Hunter, 2017 Lynskey Backroad, 2017 Raleigh Gran Prix, 1980s Bianchi Mixte on a trainer. Others are now gone.
SP hubs can be wired either way. It produces AC so there is no + or -, but for some reason some manufacturers have indicated that there was a plus or minus.
Shimano hubs are grounded to the fork, so that is an issue with a Shimano hub if the light is also grounded to the fork (I wasted hours learning about that). But your SP is not grounded to the fork, so does not matter.
I think the reason that some manufacturers had a + and - was because that is a way to figure out how to wire things if components are grounded to the fork or frame.