Swiitched live feed?

[mr self destruct]

Use a 4 pin relay like this:


Terminal 30 connects directly to the battery via a fuse suitable for whatever the intended use.
Terminal 87 runs to whatever you're powering (sat-nav, charger, spotlights etc.).
Terminal 86 comes from whatever you use to activate it (i.e. the sidelight switch, or a toggle switch, or the ignition if you want).
Terminal 85 runs to earth.