Powerdynamo, the function of the blue (blue/white) wire

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Technical Help



the famous blue wire ...

All our CDI ignition coils and the advance control unit for internal trigger systems s have a blue (sometimes also blue/white) wire. This wire commonly called "kill wire" is for switching the system off by shortcircuiting the internal capacitor.

This function is needed as magneto based CDI systems would otherwise run until you run out of petrol (gas).

We get many questions relative to this wire and its connecting.

And there are potentially many ignition problems related to it.

As explained, this wire, when connected to ground, shortcircuits the capacitor inside the coil (or advance for internal trigger systems / only this one! not the other advance units!).
  • any mistake in wiring that leads from this blue wire to either a killswitch on the handlebar, a main switch or the switch off relay will prevent ignition. We had many instances of malfunction due to a wire caught under the driver seat, rubbing against the streering head, defective main switches, wrongly connected (rarely defective) relays.
    We have had already killswitches mounted on powder coated handlebars which prevented good ground. Also there have been killswitches with very bad contact, giving only high resistance contact resulting on one hand in failure to cut off engine, and on other hand ignition problems during engine run.
    There have been customers connecting a tacho (revolution meter) to this wire, also resulting in problems and possibly the death of the instrument.

    So, as first step when confronted with some ignition failure, disconnect this wire directly at the ignition coil (or the advance)
  • it may also be the reverse problem that ignition does not stop, even though the blue wire is connected to chassis-ground. In such cases there is a bad electrical connection between frame und engine. Solution is to add a wire between chassis and engine block.
  • never introduce voltage into this wire (actually neither any of the other wires either!). for reasons not knowns to us we had quite a few customers who connected thism wire to battery plus. this will lead to failures.
  • as the condenser is - during engine run - constantly charged with between 300 and 500 volts, this voltage is also present on the wire. Thbis is not any really harmfull voltage, but it still may produce considerable pain and  alarm to the driver when wrongly handled.

    Wrongly handled means either directly touching its open end during engine run or having it connected to a kill switch mounted to a handelbar that has only insufficiant ground contact - say due to powdercoating of the frame.
  • when the blue wire is connected to a push botton switch, engine may be restarted by anyone kicking it on as the main lock is bypassed!
  • using a switch off relay is the best and safest method to connect the kill wire. Chances of touching it during run are next to nill and there is no risk that someone can kick on the bike without the keys. However the relay works only in a battery environment.
    For wiring the elay see this plan here

Follow typical wiring instructions for 2 stroke (only CDI coil) and internal sensor advance controled (4 stroke) systems showing different blue (kill) wire connection options

Click diagrams to enlarge.

Wiring diagram for relay method 2 stroke Wiring diagram for Killswitch method 2 stroke

Wiring diagram for relay method 4 stroke Wiring diagram for Killswitch method 4 stroke

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