The industry standard is for keyed switched power.  Some companies offer a switch to control the power pin, some have an option for live too.  A relay triggered with key power from the keyswitch, fused at the battery feeding the 7pin works fine.  There is also nothing wrong with an inline fuse at the battery feeding direct to the connector.  The primary reason for insdustry standard of "keyed" is so power is off when tractor is off and thus cannon drain the battery.  We have ours on a switch and the switch is on most of the time.