Best place to wire a new tach

So I was looking at the wiring on my 68 Barracuda and was trying to figure out the best place to tap in to for an aftermarket tach. The signal wire I will just put on the dist. post of the coil. I'm thinking about tapping the orange wire to the radio for the dimmer. What is a good keyed 12v for the tach power? I was thinking radio there as well but would it be the white wire or the red with tracer wire? Is the steering column ground not "noisy"?