Wired up the DPDT mini switch earlier tonight and that works & sounds best out of all the combinations tried so far.

Thanks guys for all your ideas, guidance & assistance.

Next job is to dig a bit more timber out in the control plate cavity as there is a square plastic terminal block for belcat pre-amp with lots of wires coming and going that is preventing everything fitting in an already cramped space. Don't own a dremel and not keen spending the coin for just this one job. Might have to use a chisel instead unless someone has a bright idea for cutting/recessing at 90 degrees inside a 30mm wide trench which is just on 38mm deep?

For it it sit vertical, thickness is about 6 or 7mm thick whilst horizontally I would need to go about 18 to 20mm deep and drilling in via jack socket hole seems most logical way to go? Will ponder this for a few days before attacking it.