On my '01 I tapped off the passenger side battery to a fuse block. One fuse (15A) goes over the back of the engine on the firewall lip (tied up to the regular harness bundle) and into the customer access wire. I hooked up the in-cab end of the customer access wire to the main terminal of a Bosch-style relay, and the normally open terminal goes on to my CB. I tapped the windshield wiper circuit from the dash fuse block to run the relay coil because it is the only wire hot in both ACC and IGN. That way I can run the CB without having the key in the ON position.

Works great. No noise.

 

I meant "big power" not 30 watts.
I mean like hundreds of watts.