Go straight back to the battery and put a inline fuze in. As far as location you likey will have to put it on top of the cab to prevent glare off the windows. On my 590 if you hit the signal light left and righ it throws on great side lights. The lights are pretty good except they do not shine a long ways forward.
Mudhole, I put a 50" curved bar on on S88 Gleaner. Fit like a glove, no glare on windows. Looks like you have a bar on top side of the cab to hang onto while washing windows. I would mount yours to it like I did. I ran a power wire direct from the battery as SouthernSK said but I didn't want to get a wire into the cab and mount a switch so I put a relay in the line and tapped into a wire going to another set of lights so when I flip the switch to turn them on that power pulls in the relay and turns on my light bar. Used heat shrink connectors and sealed it up good and had no issues. I also put to a 20" light bar on each side of mine about 4 feet above the ground shining out to side. When I turn my lights on I can light up the whole field. I turned all my factory lights on, AC and anything else electrical and checked amp load to be sure my new lights weren't going to over load the alternator. Even adding the 3 light bars I was still 25 or 30 amps below rated output of the alternator but I don't even turn some of the factory lights on now with the light bars on.
We just put lightbars on a 750 and 760. There is already wiring under the mirror arms on both sides......take the top cover off with torx screws and there will be empty plugs on both sides. The 760 has a JD globe so I mounted 2 smaller lightbars on either side of it just screwed into the roof. The 750 has AgLeader and there is a bar that overhangs the front of the roof so we just drilled 2 holes through the bar and hung a 50in curved from it. Very easy installs. Also while you are under those covers there is also an additional wire for a second beacon so I made mounts and bought beacon power posts and mounted a second beacon on both machines.
I would be very careful about connecting a lightbar into preexisting wiring unless you KNOW that there was enough extra current carrying capability. Lightbars (even LED) draw a lot of current. And lets face it...most MFG's design their wiring (and everything else) for "just enough" for the OEM system. With the cost of OEM wiring, I'd hate to burn any up. That's why I strongly encourage always going straight to a main power stud (Like the one into the cab, or in the fuse compartment. IMO, going directly to the batteries is not usually necessary.) Use a good inline fuse, and then a relay to turn it on with the other lights, if desired.
Doing this protects the original wiring from overload. Now, if you are replacing older lights with LED...thats fine, as you are actually decreasing the current load in most cases.