"These 3 lights have 12volt supply to them but it appears the line to ground is the wire which is connected to the master shutoff, and this is where the problem is."
Are some of these "3" lights in the wet bay? And FWIW, ground wires are typically white. Really: Are there white wires connecting to your master battery cut-off-switch (in the battery bay)?
Robi & Dale ---- Go Navy ----
2016 Winnie TOUR 42'
Tow: '08 Buick Lucerne