The power feed for the brake lights will be an orange wire. Without the accessory fuse block, it should go to the headlamp switch, terminal S. That terminal should be hot all the time. With the fuse block, it would go to the Stop Lamp terminal, I would have to check the accessory wiring diagram to be sure if that is constant power or not, but I don't think it is.
Running constant hot to the brake light switch will not be a problem, most modern vehicles are wired that way. Only time it'll be a problem is if the switch fails in the "on" position.
