ready brake indicator light - where to tap into

My coach was setup for CB radio (which I don't have or want). I tapped into the CB power wire. It's been so long, I don't remember whether that wire is powered all the time, or only when the ignition switch is on. Makes no difference; I only need to see the Ready Brake indicator when the ignition is on. It works great.

That indicator light uses very little power, so I think it would work fine for tapping into your radio power wire.