How to access ignition switch?

Hello Guys,

I have recently purchased a tachometer and am in the process of installation on my 1972 Plymouth Duster.

The installation requires running one wire to the ignition switch and wiring it so that when the key is off, no power is sent to the tach, but when the key is in the on position power is supplied.

So, how do I get to the ignition switch so that I can wire in my tachometer? Whats the best way to get to the switch?

Thanks guys, any help is appreciated.

Jon P.