Joined: Aug 2010
Posts: 12,730
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.
The SP is not grounded to the frame like the Shimano hubs are. I learned that the hard way, I started with an SP hub on one bike. I assumed all hubs were not grounded to the frame. Then I got a Shimano hub and put it on another bike, and wired that bike the same as my bike with the SP. After a few hours of total confusion, I realized that the grounding was my trouble.
You already figured out that the Shimano and SP plugs are interchangeable, I mention that in case other readers do not know that.