Just to clarify, The other 3 Regular Toggle Switch Positions work as they did before the mod? Full Bridge Humbucker, Split Middle Position, Full Neck...
that sounds like it's wired correctly.
something i just noticed on your picture, the Bridge "G" Solder Pad looks like it's bridged to the "W" Solder...
There are different revisions for the JP 3 Way Toggle Switch, i'm not sure if the wiring has changed with the revisions.
my guess is that instead of...
Music Man JP7 PDN 2012 Honey Roasted #F20403
Music Man JP6 PDN 2013 Emerald Green Sparkle #G68213
Music Man JP6 PDN 2014 Neptune Blue Roasted #G71474
Music Man JP6 PDN 2016 Starry Night #G77086
Music Man Bongo 5HH PDN 2015 Vintage Tobacco Burst #F44860