I want to wire extra brake lights into those empty rear sockets
Before you start
There aren't any bulbs in the pods next to the brake light, so adding two extra bulbs there makes a huge difference in how bright the tail/brake lighting is.
Please note: The standard method of doing this mod has long been to use the Conduct-Tite #85803 2-wire sockets, then solder a ground wire on them. Dorman/Conduct-Tite (same company) now makes a 3-wire socket in this size. It's part #84725, and comes with a backing plate you could use instead of glue or melting the plastic around the base. Using a 3-wire socket eliminates the need to solder on an extra wire.
They are available at Advance Auto in the East and Kragen/Checker/Schuck's out West. Remember that this is somewhat of a specialized product. Plan ahead, as your store may need to order a pair.
Another note: Make sure you test the wires on both of the new sockets before you hook them up. They're made in who-knows-where, and there have been reports that wires of the same color didn't necessarily perform the same function. A potential time-saver from N250RC FAQ.
The short version
It's very easy to do.
It's cheap, probably under $6, and it makes the back of the bike look bigger. It also makes you safer.
This shows how to run the wires for the additional brake lights.
Putting flashing lights in the pods
You can put Hyper-Lites (LED modules with flasher) in the extra pods. You can see the installation and a demonstration here. They're very effective, plus they give you extra running and brake lights if your incandescent center bulb goes bye-bye. $80 or so shipped. Get the generic dual-function model (for running and brake lights) from this page. They may not be as easy to install as the Kisan, but they're cheaper and provide a number of additional benefits.
For installation in the two spare pods, it's recommended to undo the two bolts holding the rear taillight on the bike and install the Hyper-Lites with the light assembly off the bike. It's a very clean installation; you can hardly tell it's there until the extra lights come on.
A little more detail, with photos
Putting extra brake lights into the rear pods is extremely simple, but if anyone is on the fence about doing it because they are afraid they won't be able to, hopefully this will help them. Doing this mod will really make you much safer.
Before you start, you should have at least the following:
For help with the electrical connections, see the small diagram (above) or the EX250 wiring schematic. Printing out the FAQ is also helpful.
For the first step, getting the rear light fixture out, you need to remove your seat. Then find the two bolts just below the grab handle (inside the body). These are the two 92015 nuts in this diagram. Remove them.
You'll also need to disconnect the white plastic harness connector located on the wires before pulling the fixture out.
After you've done this, the fixture should pull right out. It may be slightly stubborn; make sure you pull it out somewhat straight, or it can get caught. Next, there should be 4 screws holding the red plastic lenses onto the fixture. You should remove the screws and take off the red lenses. Be careful not to lose the little rubber gasket that goes around the big main red lens (it may just fall off... You can use very conservative amounts of super glue to affix it to the red lens permanently, if you think it necessary.) Here's the taillight assembly before modification.
Now for the trickiest part... Coming out of the middle brake light socket you'll find one blue and one red wire. The blue is your brake light, and the red is your running light. The black wire attached to the outside is the ground. The sockets, if you get the Autozone ones, will have 2 or 3 black wires coming out of each, so you'll have to determine which is which... To do this, take your battery (or small 9V battery) and your two new sockets. Touch the metal base of each socket to the negative pole and touch the positive pole with the wires coming out (one at a time). One of them will make the light brighter than the other. That will be your brake wire, and the other wire will be your running light wire. Put a loose knot in the brake wire of each socket, or otherwise label it, so that you remember which is which when you reassemble it.
At this point, you can install the sockets into the empty holes you'll find on each side. Sometimes they don't snap in enough to be satisfactory, so you can put some epoxy in with them to get them nice and stable. You may need to sand off the lips around the holes (left) or enlarge the holes (right) somewhat in order to fit certain kinds of sockets.
Now you will need to snip the middle (brake) light's wires about halfway between the socket and the white harness plug. Once you've done this, you will want to strip all the ends of the wires on all the sockets and the harness plug. Essentially, you will need to take the blue wire from the main light, the blue wire from the harness plug, and the two black wires you've determined to be the brake wire on the new sockets and solder them all together. Repeat the process for the red wires and the corresponding black wire from the two new sockets. You can also use crimp connectors. These came with heat shrink tubing.
If you have 2-wire sockets, solder the extra two lengths of wire you should have to the bodies of the new sockets (similarly to how the ground comes off of the main light). Once they are soldered on the sockets themselves, take the other ends and solder them together with the ground wires from the main light and the detached socket.
You can use heat shrink tubing to seal the 3 solder joints. Electrical tape is a poor substitute. Now everything should be connected... Put the bulbs in. Reassemble the fixture, putting the red lenses back in place. Place back in your bike, put the two nuts back on, attach the white wire harness and you should be ready to ride.
Here are some pictures of the finished light fixture, before the lenses are put back in place or it is put back in the bike.
And some shots of it in place and working:
Changing the lens color
If you don't like the red pod lenses, there are a few other choices. Keep in mind that there is a very high chance that these are illegal. We're not going to tell you your own local laws; some things you have to do for yourself. Note, however, that US federal law, which nearly all states follow, mandates that there must be at least nine inches between the lights, if they are being used for turn signals. The EX250 can't make that. These aftermarket lights are also not DOT-approved. You'll have to decide how you think your local law enforcement and state inspection departments will react to this modification.
The law: US Code of Federal Regulations, Title 49, Part 571, Standard 108 states that turn signals must be amber or red and must be at least 9" apart, center-to-center. If signals are red, their edges must be at least 4" away from the edge of the tail light.
Clear Alternatives also makes kits for the EX250.