My LED turn signals don't work right
If you have converted your turn signals to LED bulbs, you probably have two problems: The signals flash too fast, and all the bulbs flash at the same time.
Fixing flash rate
This is the easy part. You need to replace the flasher that came in your bike with an electronic one. An electronic flasher (aka turn signal relay) will make your flashers blink at the same rate no matter whether they are LED or incandescent. The flasher that came with the bike doesn't work with the low current demands of LED lights. The pictures show the location of the stock flasher.
The stock flasher is Kawasaki part number 27002-1101, Denso part number FE218BH, although you shouldn't need this information when looking for an electronic replacement. Since there are 2 wires on the bike to connect to the flasher relay, most any 2 wire electronic flasher should work for the Ninja. You should be able to find one at your local auto parts store. Maybe. If you get a blank look when you ask there, try one of these:
To wire your new flasher, the wire that is orange with a green stripe is 12 volts in from Fuse 1 in the junction box. The solid orange wire runs out to the turn signal switch.
Connect to the stock wires using crimp connectors and heat shrink wrap.
Connectors that are sold with heat shrink already on them are very convenient.
Why the stock flasher doesn't work with LEDs
Older vehicle flashers were mechanical. They had a small piece of springy metal in the relay body, and as it heated up from current flow it flashed the signals. Mechanical flashers will increase or decrease in rate as voltage or current changes because the springy metal bit heats up at different rates.
The stock EX250 flasher is solid state, but it's fairly simple - just a chip with a cap and a resistor or two. It doesn't use a timer, though. This is why its flash rate varies with bulb load, like an old mechanical flasher. With mechanical flashers, as more bulbs are added, the current through the heater element increases and causes it to heat faster, breaking the contacts faster and resulting in a faster flash rate. The Ninja's solid-state flasher reacts the opposite, flashing faster with the reduced bulb load from lower-current LEDs. Fixed-rate flasher modules (like the new one you're putting in) use a timer to regulate the flash rate independently of bulb loading.
Fixing "all signals flashing at the same time"
When this happens, the signal indicator bulb in the dash is the culprit. The stock Kawasaki wiring relies on the opposite indicator (signal) filaments to provide the ground for the flashers (the bulbs on the right side ground the left, and vice versa.) LEDs don't provide as much resistance as incandescents, so enough voltage gets through the dash indicator bulb to light the opposite side indicators.
The answer to this problem is to make two separate circuits for the turn signals. There are two ways to do this. Pick the one you feel most comfortable with.
Note: If either the two front signals or the two rear signals still have incandescent bulbs, modifying the gauge cluster bulb is not necessary, but you'll still need an electronic flasher to regulate the flash rate.
Using diodes is probably an easier way to do make your new signals work than the LED method described below. It should be easier for most people to solder wires and make a ground using a ring terminal than to fiddle with small parts inside the gauge cluster. Another nice feature of this modification is that any cluster will work, so if the cluster needs to be replaced for any reason, the wiring modification will still be on the bike.
A diode is a simple one-way valve. It only allows electricity to flow in one direction. This will keep the two turn signal circuits separated. More about diodes
If you haven't use diodes before, this may seem a little complicated. But all you're really doing is rewiring the light bulb. The portion of the schematic shown below shows how this setup works. The two wires run into two diodes. These are then wired together and sent to the bulb. The 'one-way valve' on the diodes keeps the electricity from flowing back through the opposite signals' wire, as it does in the stock wiring. The bulb is then grounded with the leftover grey wire. So, instead of having two hot wires going into the bulb, there is now a hot and a ground, just like a normal bulb.
To start, get two diodes, part number 1N4001. These are available at Radio Shack or other electronics stores. This is a general purpose diode and should be easy to find. Then you can just follow the directions on the pictures.
At the six-connection plug under the headlight, use a paper clip to remove the green and grey wires from the male side of the plug. In stock form, these wires bring power to the "your signals are on" dash light. You are going to splice into these wires. When you do, leave enough wire on both ends to make the splice, ie... make your cut several inches back from the connector.
Set aside the connector end of the wires that you cut off for now. Take the green and grey wires coming from the harness and solder the anode (+) end of one of the diodes to the green one. Solder the anode of the other diode to the grey wire. Then you need to solder the cathode (-) end of both diodes together to the end of the green wire (with connector attached) that you cut off. What this does is make one hot wire out of two.
You still have one wire left over: The grey one with the connector on it. You need to make this wire longer (solder or crimp connector) and put a ring terminal on the end. This is now the ground wire for the light bulb.
Find a bolt on the frame to hook the ground wire to. Make sure you have heat shrink wrap on all the splices. Reconnect the two connectors at the six-connection plug and check to make sure that everything works right.
This method uses LEDs placed in the turn signal cluster in place of the stock "your turn signal is on" incandescent bulb. You'll end up with two separate LEDs, each fed 12V through the turn signal switch. Both are provided a ground from the Yellow/Black ground wire in the cluster.
To make this change, remove the instrument cluster:
Now that you're down to the gauge cluster, separate the white plastic back housing from the black front housing by removing the phillips screws from the rear. (Pay no attention to the circles in this photo; in FAQ we use what we have.)
Pull the two halves of the cluster apart. All three analog gauges are now visible. If you gently pry on the colored plastic of the four indicator bulb diffusers (red, blue, yellow, green, aka 'idiot lights') you can get at the area the indicators live in. Now tap into the Yellow/Black wire wherever is the easiest for you: The high beam bulb, the tachometer, the water temp meter or any of the three gauge illumination bulbs. You just need to choose one; this is your ground. (Yellow and black wire is ground throughout the bike.) Use crimp connectors as detailed above, and run that new wire into the turn indicator bulb area of the dash.
You now need to attach two 12 volt LEDs to the stock bulb socket. Solder the anode (+) end of one LED to the green wire and the anode of the other LED to the grey wire. Solder both cathode (-) legs together to the black/yellow wire for ground.
To mount the LEDs, test fit one into the bulb housing first. If one leg of the LED fits nice and stays in after given a tug, call it good. If not, solder the LED anode (+) legs to bits of solid wire and then shove the wire into the bulb housing. LEDs weigh almost nothing, so once they're in they're probably not going to bounce around much. Use a prodigious amount of electrical tape on each leg and then the whole assembly, to ensure that nothing moves or shorts.
Put the 4 colored plastic bulb diffusers back in place, button up the cluster and reattach to the bike.
Diagram for this mod. Stock is on the left and LED is on the right.