The wires will either come out the bottom of the light bar, or through a hole in the side of the lightbar. KC lights come with a nice harness, so if you go that route you won't have a bunch of loose wires exposed.
Getting the wiring harness into the engine compartment isn't too bad; I routed mine under the windshield frame (you can easily remove the wiper arms & that small vented body panel under the windshield). There's adequate clearance to put the wires there. I drilled a hole into the engine compartment, and used a grommet to protect the harness. Then you can install a fused link to the battery, and follow other wires thru an opening in the firewall to connect your switch. I can send pictures if you'd like...it's easier than it sounds.