Your light kit should come with instructions on how to install it. Mine did, but my install was different than the bike in the instructions, because I was using only battery power. I saved money by ordering the kit that I did, but the installation wasn't quite as simple as it could have been. It wasn't at ALL difficult though. If I had a CRF 230, the install would have been 100% plug and play. If I was using a lighting stator, also 100% plug and play.
Here is my bike, pre-kit, with the side number plates and seat removed (click any pic for a larger view):
My Baja Designs kit came with a Headlight (with mounting straps), an LED tail light assembly, a Hi/Low/Off switch with a kill button, a hydraulic brake switch, and wire harnesses. I also ordered a mirror with my kit. The only other thing, besides DOT tires, that I needed now was a horn. I've read about people using bicycle horns, but they were all about $30, and I doubt that they would get the attention of a motorist. I went down to my local AutoZone and picked up a $15 car horn, and it's LOUD.
I used a spare bracket from my lighting kit to mount the horn to my upper triple clamp, using the bolt that used to hold my number plate on.
Here it is mounted and wired up...did I mention this horn is LOUD?
With the GPS installed, the largest flap of the bar pad cover hides the horn and wiring. I used tape on the horn connections (heat shrink on everything else) The tape will keep the occasional water splash from getting my connections wet. I wired the horn to the battery like everything else, using the stock kill button as my horn button.
My system does not use chassis ground. Every connection goes back to either the + or - side of the battery. Here is how I mounted a small SLA battery in my airbox with heavy duty velcro straps. The battery just barely touches the filter and it touches the bottom of the seat enough that the seat helps hold the battery tight when the seat is bolted on. Works great. If you don't like the velcro idea, don't use it on your bike. It's your bike, and your money. I have seen some aluminum plates at my local cycle shop that I might try, but for now, velcro works great. It's also easy to swing the battery out of the way for maintenance.
When I wired in my battery, I also wired in a Battery Tender Jr. plug. I used male spade connectors on each wire from the Battery Tender plug (snipping off the stock ring terminal connectors). I used female spade connectors for the lighting kit battery connections (again, snipping off the stock ring terminals). I slightly expanded the female spade connector so that it would fit over both the battery's male spade AND the Battery Tender spade. I did this on both the + and - side of the battery.
I keep the Battery Tender plug tucked away, with the protective boot on it, when I'm riding. When I'm parked, the bike gets plugged in to the Battery Tender, and stays charged. Here it is, plugged in.
The only other deviation from the instructions I ran into was installing the hydraulic brake switch. I had to unbolt my rear master cylinder to get the 90 degree plug to screw on. It was easy to remove and reinstall.
Here is a pic of everything wired up and working. The tail light has a built in license plate light. With the brake applied, it lights up my garage...it's very bright. The head light works great too, even off straight battery power. It's as good as any OEM motorcycle headlight I've ever seen, and better than some. The battery I used will keep the lights on (full strength) for at least an hour. I don't think riding an MX'er on the road anywhere close to that long would be much fun for you, or your bike. But, this will get me 10 minutes down the road to nearby trails, legally.
With all that installed, it was time to get inspected. On my second try (see "Getting Legal..." for why), I had my inspection sticker. I also installed a GPS system on my bike. (HP iPAQ 310). It works great as a speedo and is easily removable once I get to the trails. I haven't found a way to mount it sturdy enough for trial use yet. But for street, even agressive riding and bumpy roads, it holds up great.
...now I was just one step away from being street legal. A trip to the local Tax Office, and I had my plate and registration. I didn't really run into any issues- just having to add an initial here and there, and putting my SS# on a form in a blank that I missed. I did notice that the clerk used the Out of State Inspection form instead of the VI-30A. Could have been just this clerk, but ask your inspector for it, just in case. The person that inspected my bike said that I might need both. I'm glad he gave me both, or I'd have to stand in that line again...
In the end, the whole process, from buying the bike to getting the plates took about 2.5 weeks. If you have a clean title already, you could cut it down to a few days. Depending on how fast you had your lighting kit and other parts shipped, it could be longer.
As far as cost, I have about 2K into the whole project. I was not able to find a Dual Sport bike as nice as my cr250, with plates and a clean title, for that price. I looked around, and Dual Sport bikes in this kind of shape, without all the aftermarket goodies, were all in the $2500 range or higher.
2 strokes are generally cheaper to repair/rebuild than 4 strokes. That was one of the main reasons I wanted a 2 stroke. It's a bit more maintenance, but there's just something about that 2-stroke power.