30 MCN I For Enthusiasts MCNEWS.COM
HOW TO READ
In our third and final segment, things get yet a little more challenging. The wiring diagram shown is pretty typical of late 1990s technology.
The bike for this exercise is carbureted
and has an electronic ignition module
that uses a throttle position sensor. A
one-piece alternator, with internal voltage
regulator, is used for the charging system.
Five fuses distribute power to various
components. There are two relays: One
is used for the side stand, and the other
is the starter solenoid that connects the
battery to the starter motor. There are
several components used to prevent the
engine from starting unless the clutch is
pulled in and the side stand is up.
Instruments are standard: speedometer, tachometer, fuel gauge and
indicators for neutral, high beam and
turn signals. Wire colors are indicated
by letters: G = Green, Br = Brown, LBl =
Light Blue, O/Bl = Orange with a Black
stripe, etc. A good visual aid to assist you
in answering the questions related to
the diagram is to draw a simple sketch
of just the circuit that is being studied.
This will help by removing all the other
wiring clutter that tends to get in the way
or make the circuit confusing. Answer-
ing the following wiring diagram related
questions will help you to sharpen your
wiring diagram reading skills. Good luck!
Q1. The four instrument lights (two in
the speedo housing, one for the fuel
gauge and one in the tach housing) do
not light up when the key is in the ON
position. The oil pressure light (marked
with an “O” in the tach) stays on even
with the engine running (the engine
has oil pressure). Which fuse powers the
instrument lights and what is the wire
color at the ignition switch that provides
power to the instrument lights? What
common electrical problems could be
causing the oil pressure light to remain
on with the engine running?
Q2. The motorcycle has a no-spark
condition and there is no power at either
of the ignition coils when the ignition
switch is in the ON position. Trace the
path that power takes from the battery
to the ignition coils. Include the wires
(colors) fuses, switches and relays used
in this circuit.
Q3. The brake light does not come on
when the front brake lever, or rear brake
pedal are applied (ignition switch is in
the ON position). What would be the
most common causes of this problem?
Trace power from the battery, through
the brake switches and to the tail/brake
light. Include wire colors and electrical
components that are used in this circuit.
Q4. With the key in the ON position,
and the engine stop/run switch in the
RUN position, the starter doesn’t operate
when the start switch (top center of
diagram) is pressed. In addition to a bad
start switch, what other components
could cause this problem? How can the
starter solenoid (lower right of diagram)
be triggered (causing the starter motor to
operate), using a jumper wire connected
to the battery positive terminal?
A1. Starting at the battery positive
terminal, the Red wire at the main fuse
powers fuse No. 5 (taillight) that, in
turn, powers the instrument lights. The
wire from the fuse No. 5 is Orange/Blue
and at the connector, located next to
the ignition switch, it changes color to
Green, where it then goes to the ignition
switch and through a connector (below
the instrument cluster) where it powers
the four instrument bulbs. There are
two reasons that the oil pressure light is
on with the engine running: the Green/
Yellow wire from the light is shorted to
the frame/engine case (grounded) or a
faulty oil pressure switch.
A2. Starting at the battery positive terminal, the Red wire has 12 volts, which go to
the starter solenoid and main fuse. From
there, the Red wire goes to the ignition
switch. When the ignition switch is in the
ON position, all the wires at the ignition
switch will have 12 volts, including the
Orange wire that goes to fuse No. 3 (igni-
These theory-to-practice exercises will help you to see actual results.
> text and image
by Tracy Martin