Basic electrical failures

No Source; Open; High Resistance; Short; Ground


The Main source of power on a Motorcycle is the Battery.  The most common electrical failure is the absence of power, or a discharged battery.  The battery does not need to be fully discharged for circuits to stop functioning, as most circuits require a minimum voltage to operate.

Except for off-road bikes, most motorcycles use a 12 Volt Battery, and a minimum of 10.5 Volts is necessary for any system or circuit to function.

One system however will require a fully charged battery to operate: The Starting System.

(Pure off-road bikes often are powered by coils coupled with magnetic rotors, and are started with a kick start.)


A circuit cannot function if any part of the circuit does not allow electricity to complete it’s full Path.

Starts at the source, powers the Load (or component), and returns to the Source.

Broken or Frayed wiresExamples of Opens:

  • Disconnected wire
  • Dislodged connector
  • Burned Fuse
  • Broken switch
  • Burned Load device
  • Cut wire (often occurs at joints)

High Resistance

Corrosion and Sulfating

Over time, any motorcycle will accumulate corrosion in it’s connectors.  The battery posts and connections are most susceptible to corrosion.  A bluish sulfate powder will form if no maintenance is done on the battery.  It is easily removed, by simply pouring water over them, while the battery is disconnected.  The posts should be free of such sulfate.  For the connectors, dipping them in a cup of water is most efficient.  Of course, once the sulfate is removed, drying the surfaces using an air blower is a must.  Reassembling with water will cause the connections to sulfate all over again.  It is recommended to apply a dielectric grease after assembly to prevent water from entering again.  Most connectors on modern motorcycles are waterproof, and the seals should be inspected, and replaced if necessary.

In switches corrosion or burned contacts will cause high resistance.

Loose crimping of wires to connectors can also occur over time. In addition vibrations can cause a wire to fray and loose it’s conductivity.

Poor connections can cause high resistance. Loose connectors may need replacement. Pin type connectors are very prone to becoming loose, mostly by poor manipulation from the owner or the technician. Carelessly probing the front of such connector can cause a new failure.

Any electrical system using a brush type connection will eventually fail over time. Brushes, often made of carbon will wear out and cause a high resistance (starters, alternators).


If any part of the positive side of a circuit (before the load device) comes in contact with the negative, a short will occur. The fuse will blow (melt), and the circuit will stop functioning.

Merely reinstalling a new fuse without troubleshooting, will cause the new fuse to melt.

Installing a higher Amp/hour rating Fuse is the worse remedy one could even think of.  This time the wires or the whole harness could melt.


This type of failure is often called as a loss of control. It can only occur in a circuit where the switch device is on the negative side of the circuit.  Yamaha likes negative switching, most other manufacturers prefer the switch on the positive side.

Some Charging systems are switched on the negative side, as do circuits with a push type switch (starter, ignition cut off…) Some safety devices are often switched on the negative side.

Troubleshooting Shorts

Once the fuse is blown, replace it by a high power bulb (brake light bulb will do).  A bulb in it’s appropriate socket with two male spade connectors can be used, and plugged in the fuses place.  If for a normal size fuse, use large male spade connectors. For Mini fuses, small male spades.

  • Make the connection while the negative of the battery is disconnected.
  • After identifying the circuits that were inoperable, make a diagram to identify the load devices protected by the fuse.
  • Reconnect the battery.
  • If the bulb comes ON brightly, either the short is prior to the Main Switch or the circuit is always powered originally (rare: clocks, memory systems…)
  • If the bulb is off, turn the main switch ON, if it still isn’t lighting, you may be working on an intermittent circuit: Horn, turn signals, high beam, brake light, etc…)
  • Power the appropriate circuit: If the bulb is bright, start disconnecting load devices of the circuit until the bulb becomes DIM. The last load device’s positive side that was disconnected is where the short is.
  • Inspect and repair that circuit, including the load device.
This entry was posted in Moto Tech and tagged , . Bookmark the permalink.

Leave your opinion