Introduction: Honda Metropolitan Alarm/Remote Start Install
Look on Amazon and if you search for "2-Way Motorcycle Alarm", you will get dozens of results from different vendors. While they are branded differently, they appear to all be based on the same hardware and share the same installation instructions and color coding.
I picked up one of the variants from Amazon to install and this is the wiring diagram that came with it. For ease of installation, I added the notes matching the Brain wire color to the wires of the 2005 Honda Metropolitan. Over the years, it appears that the Honda Metro wiring diagram has remained fairly consistent and this should work for other model years (and maybe even the Ruckus as well), but your mileage may vary.
I highly recommend getting Posi-Taps and Solder Seal Wire Connectors. While they are a bit more expensive than your cheaper taps, I find them to be more reliable and much easier to use (especially if you tap the wrong wire by mistake).
Step 1: Full Wiring Schematic
This schematic comes in handy for installation and trouble shooting. As you can see, all the wires you need are 100% accessible behind the headlight and front, center panel of the scooter. No need to rip into the back end of the scooter to get this done.
Step 2: Red Wire
The Red wire from the Brain is connected to the Red/Blue wire which is located behind the Ignition Switch Housing. This is a constant +12v source.
Step 3: Brown Wire
The Brown wire from the Brain is connected to the Red/Green wire which is also located behind the Ignition Switch Housing. This is the power source which is +12v with key lock (accessory power)
Step 4: Black Wire
I grounded the Black wire from the Brain, to the frame of the scooter. Any attachment point will work.
Step 5: Yellow Wires
For the Yellow wires from the brain, I attached one to the Green/Orange wire (the brake light) and one to the Green/Yellow wire (the head light).
NOTE: These lights did not flash when triggered until I replaced the standard bulbs with LED versions. Apparently the pulse out of the Brain is not strong/long enough to flash a standard incandescent bulb.
Step 6: Blue Wire
I connected the Blue wire from the Brain to the Yellow/Green wire. The Yellow/Green wire is connected to the thumb starter on the handle bars. By connecting here, you bypass the hand brake circuit that requires you to hold a brake before the starter will crank.
Step 7: Pink and Gray Wires
This one is hard to see, but I cut the Black/White wire on the scooter and used the Solder Seal wire connectors to attach the Pink wire to one end and the Gray wire to the other. The Black/White wire is connected to the engine shutoff switch on the right handlebar control group.