I try to connect my A518 OD activating by means of switch

OK NSS is ground only. So you need a relay, or else if you are using an aftermarket shifter, AKA Hurst etc some of those have a series wired type switch. But even those are "light duty" switches, and need a relay. Modern Mopars like hemis and Magnums used Bosch style relays so that would work.