From the 2003 manual
Module – Ignition Switch / Starter
In each 2003 model there is a module installed that provides two functions: 1) ignition switch
and 2) starting. The module is located on the battery situated in the recessed portion of the top
of the battery and is held down with the battery strap (see Figure 14). The module has 5 wire leads
that connect to the electrical system. The power wire (red) is connected to the battery positive
terminal and the ground wire is connected to the battery negative terminal (see Figure). The
large green wire connects to the starter solenoid (starting function) and the large orange wire
connects to the EHC (providing power).
There is a 3-wire lead that has a JST connector at the end that plugs the module into the main
harness. The three-wire lead connects the module to the ignition switch and to the starter button
in the handlebars (see schematic for wire connections). All of the wires have a protective sleeve
with the exception of the two wires that attach to the battery. The module is a potted unit and
cannot be repaired and must be replaced if defective. There are two LED’s that are visible on the
same side of the module that the wires come out (see figure). The red LED is part of the starter
function and the yellow LED is part if the ignition switch function.
Figure 14
Module (Ignition Switch Function)
The ignition switch part of the module is a solid-state replacement of the old mechanical ignition
switch used in the past. The module takes power from the battery and provides it directly to the
EHC where all loads are attached. To turn on, it needs a small signal and it gets that from the
new ignition switch that is located in the coil cover just as in earlier models. This allows the
use of a smaller mechanical switch (see section on Ignition Switch). For 2003 models, the current
that flows through the harness does not go through the mechanical switch but from the battery to
the EHC through the module. The module three-wire lead has a small red, orange and green wire that
connects to the harness by a 3-position connector (see schematic).
Battery voltage is present in the small red wire attached to the ignition switch. The orange wire
also attaches to the ignition switch. When the orange wire touches 12 volts it activities the
module and power flows through the EHC supplying power to the system. The green wire is used for
activating the starter (see section on starting).
The module has fault detection l detect if there is an open or short circuit on the load side of
the module (large orange wire going to EHC). If there is an open or short circuit while the module
is turned on the yellow LED will turn on. The module also has fault protection built in and if the
current gets too high it will go into a fault mode and limit the current and light up the LED.
During a short circuit fault mode the module limits the current not by shutting down completely but
it goes into a pulse mode and limits the current by very fast switching. Current still flows but at
a lower level. The short circuit fault mode switching is very fast but can be seen by looking at
the LED and it will flutter.
If the yellow LED is on this is how to tell if the module is sensing a short or open circuit. Also
when the module is in a short circuit mode (switching) anything on the bike that is turned on
(example: neutral indicator) will blink and this is another way to tell that the module sees a
short circuit. The module is also sensitive to low levels of current. For example when the ignition
switch is turned on, the headlight and taillight will come on but if the headlight was unplugged
then the yellow LED will light up because the new 2003 taillights which are LED do not draw enough
current to tell the module that there is not an open circuit. This can be useful in troubleshooting
headlight failures.
When starting the motorcycle, the yellow LED will light up because the EHC relay (headlight relay)
will turn off the headlight while the starter is engaged, so for a short period of time the module
thinks that there is an open circuit because the only load on it is the taillight. Refer to the
schematics for module wiring.
Big Dog Motorcycles, LLC
Rev. 11-2
Service Manual
Electrical – Page 11
Big Dog Motorcycles, LLC
Rev. 11-2
Service Manual
Electrical – Page 12
Ignition Switch
For 2003 models there is a new ignition switch. The new switch is much smaller than in the past and
as stated in the module description it no longer conducts current to the EHC. The only function the
new switch has is to turn on the ignition switch part of the module. The new switch plugs into the
coil harness via a two-position connector that also helps make it easy to replace if necessary (see
Figure 15).
Figure 15 - Ignition Switch
The switch plugs into the coil harness and the connector is located next to the coil tucked inside
the coil cover (see Figure 16). To remove, simply unplug the switch and remove the nut and washer
that holds it to the coil cover and the switch is easily removed. The coil cover assembly has a
disconnect and it can be unplugged from the main harness and pulled away from the bike
so that getting to the back of the coil cover is easier. The 4-inch switch lead has a red wire and
an orange wire. The red wire is always live with battery voltage and the orange wire is powered
when the switch is turned on (see schematic).
Each switch comes with two keys and those keys have a number stamped on them, example: BD42. It is
a good idea to write this number down so if the keys are lost a set can be replaced without
replacing the entire switch assembly. Part of the 2003 models will have the number stamped on the
face of the switch but for early 2003 models this number should be recorded for
later use if needed. Extra keys blanks are available from Big Dog Motorcycles.
