VW Electrics 12 volt live feed only when engine running
Look at the back of the ignition switch you will find two black wires that go to the same point on the ignition switch, these are the ideal place to tap off for ancilaries as they stay live when the engine cranks, of course it should be suitably fused. Hope that helps.
On the back of the fusebox terminal G2 and G5 are ignition switched circuits and take standard 6.3mm female blades. G8 is dash lights, handy if you want extra guages iluminated and diming with the rest of the dash. Tidyest way to do it in my opinion as you don't need to cut anything.