It is not as confusing as it first appears though, and if you trace the wires from the various switches you will soon see how it works.
There are a few non-obvious sections of the diagram that are worth looking at a bit more closely though.
You might have noticed that there are 7 separate wires in the ignition switch but 4 of them don't do anything:
- The light green wire that connects to the HOB (horn button) terminal in the switch, and the black-white wire that connects to HO (horn) don't connect to any wires in the harness
- The light blue wire connecting to the switch WL1 (winker light right) terminal and the orange wire connected to WL2 (winker light left) are connected to together when the ignition is turned off.
If you look at the Ignition Switch Arrangement table you will see that when the ignition switch is in the Off position the light green, orange and light blue wires are connected together (for no good reason, since none of these wires receive power when the switch is off). When the ignition switch is turned to On this connection is broken and instead the black/white wire in the switch (which doesn't go anywhere) is connected to the light green wire (which doesn't go anywhere either).
What's that all about? If - like me - you are sad enough to be interested, the answer lies in the wiring diagram for the contemporary C90DX sold in Australia.
This bike used the same switch but a slightly modified wiring harness:
As you can see in the diagram on the left, when the ignition is on pressing the horn button connects the horn into the live battery circuit so, all being well, it will beep as expected. But, per the diagram on the right, when the ignition is off and the horn is pressed the battery will illuminate the turn signals, presumably to brighten up the area around the bike as you fumble for your keys and the like.
I have no idea why Honda saw fit to deprive us Brits of this excellent feature.
The lucky blighters in Oz also got a buzzer that sounded when the turn signals were on, which I guess was a requirement of the legislation at the time. You can see the full wiring diagram here.
Lighting dimmer switch
The on-off lever on the dimmer switch has two functions: as well as turning on the lights it also makes a connection between the yellow and white/yellow stripe wires in the harness (I did not show these wires in the diagram above to keep it simple). Connecting these wires enables the "booster" coils on the alternator to compensate for the additional power needed by the lights. You can read more about this in the article about the charging system.
Turn signal indicator light
If you look closely at the speedometer housing on the wiring diagram there is no earth symbol (it is actually isolated from the frame by a rubber gasket that is there to prevent water ingress). So how do the indicator bulbs get an earth connection? The neutral light and speedometer light are easy to work out - they are earthed through the neutral switch and the headlight frame mounting respectively. The turn signal indicator light, however, just has two connections to the wires that carry current, one for the left side turn signals and one for the right. This works because when one of the wires becomes live the current is able to complete its circuit to earth via the element in the opposite sides unlit main bulb earth connection.
... or turn signal flasher if you prefer. This is the device that causes the turn signal lights to flash on and off. There are 3 pins: black switched live wire connects to the B/Battery terminal , the grey wire from the indicator switch goes to L/Load and the E/earth terminal is earthed to the frame at the mounting point of the rectifier.
Some cubs have a two pin relay and these work using a bimetallic strip, but the one on the z2 is uses an electromagnetic switch. Apparently there is a capacitor in the top of the case and this is is involved in controlling the time the bulbs are lit before they are turned off and on again. I've no idea how it works I'm afraid.
These electromechanical devices are designed to work with a specific load and this is listed on the top of the device.
This explains why, when one of your indicator bulbs blows, the flasher stops working properly.
The horn is connected to the battery as soon as the ignition is turned on. Pressing the horn button completes the circuit by connecting the horn to earth.
That's it for Honda C90 electrics.