Like RobS, I've the factory work light. Cost was about $38 which included everything.
I've had this light for about three years (swapped it from my 670 to my 790 when I traded up).
Installation takes about 5 minutes. The connector you plug into is under the seat. You need a combination or open ended wrench to tighten the nut. Tightening the nut is the toughest part since there isn't a lot of clearance between the tire and fender. Can't recall the wrench size, but I think it's 15 or 16 mm. Check this before installing the light.
If your usage is to plow your drive, the light is quite adequate. I had the hots to add a few more lamps..but not really necessary. Just aren't moving fast enogh to worry about more lighting. If I were going to plow on a public street (even a rural one), I would probably add more lights (and a strobe). The stock lamp, as others have stated, works off the light switch on the dash. Since you already own a 790, you know it's a multi-position switch. There are times I wish the work light was independent, since you cannot have the flashers on when the work light is on. For field use, no big deal...but on the rare occasions I'm on the road (while pushing snow), I'd like to have both the work lamp and flashers on. One of these days, I'll do something about that...
There's quite a few farms around my area. I've yet to see one of the tractors with more then two rear facing work lights. Most had only one, though. Most of the Deere's had the same light I had.
