Power wires

I'm rewiring a solid state amp. What is a good way to do the internal power wiring from the back of the amp to the on/off on the front and back again to the trafo?

My other amp uses just four wires. No extra insulation, not twisted (see picture) .

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I use double insulated wire here because it looks more beautifull and professional. If I have two wires w/o double insulation - I twist them and sometimes put into shining soft-silikone type termal-shrinkable insulation. It looks definitely better.