Replacing the EHC module on a 2003 Bulldog

smcd

Member
Hello all.

I've been trying to trace down the reason I have no spark on my 2003 Bulldog. I have -

• Replaced the Thunderheart ignition module
• Replaced the coil
• Replaced the ingition cam sensor

I have voltage to the coil, and voltage to the Thunderheart module. It seems that the EHC module is the only culprit left.


I see Wires Plus sells a retrofit kit that eliminates the EHC. The problem is, this kit seems to be designated for 2004-and-later models. Is there a similar kit that will eliminate the EHC on my '03??
 
The EHC has nothing to do with sending spark to your spark plugs. The only function the EHC does is send voltage to the Ignition module
 
Sounds stupid but have you changed the Spark Plug Wires
Are you getting a RED LED on your ignition module when you hit the run button
 

smcd

Member
Sounds stupid but have you changed the Spark Plug Wires
Are you getting a RED LED on your ignition module when you hit the run button
I haven't changed the spark plug wires. Do you think it's worth it?

I'm not getting a red LED on my ignition module. Not on the Thunderheart module, and not on the little black box that's connected to the battery.
 

Raywood

The Pirate
Staff member
Calendar Participant
Troop Supporter
If you call Thunderheart they will probably tell you that your ignition is not getting enough voltage from your battery.
How old is the battery?
 
If you are not getting the red LED on your ignition module then that is your issue
Not the module necessarily, I know you said its new but it wouldn't be the first time someone has gotten a bad new part, but likely power to the module. Like I said earlier the EHC is responsible for sending voltage to the Ignition Module to power it up. Find your power lead from the EHC to the Ignition Module and check for voltage after you have turned the key on and pressed the Run button.
 

Dakotabos

Well-Known Member
Calendar Participant
Troop Supporter
did you get a bad part? The system is pretty straight forward. Hope you can get it fired up. Did you check all your connections? Im sure you did
 
Last edited:

smcd

Member
If you are not getting the red LED on your ignition module then that is your issue
Not the module necessarily, I know you said its new but it wouldn't be the first time someone has gotten a bad new part, but likely power to the module. Like I said earlier the EHC is responsible for sending voltage to the Ignition Module to power it up. Find your power lead from the EHC to the Ignition Module and check for voltage after you have turned the key on and pressed the Run button.
Just so I'm clear, the ignition module is this? -






Not this -





I ask because I'm not getting a red LED out of either.
 
Yes the first pick is your ignition module
The second pic is the start module
Are you getting a green light on that module or no lights at all
If your getting no lights at all then it is bad and must be replaced.
 

smcd

Member
did you get a bad part? The system is pretty straight forward. Hope you can get it fired up. Did you check all your connections? Im sure you did
Yes. Checked all the connections. Checked both sensors, too. I'm pretty much at my wits end on this. I REALLY didn't want to replace the EHC, but I can't think of anything else to do.
 

smcd

Member
Yes the first pick is your ignition module
The second pic is the start module
Are you getting a green light on that module or no lights at all
If your getting no lights at all then it is bad and must be replaced.
I'm getting a green light on the start module. No red, though.
 

smcd

Member
Yes the first pick is your ignition module
The second pic is the start module
Are you getting a green light on that module or no lights at all
If your getting no lights at all then it is bad and must be replaced.
One thing I haven't mentioned is that there was an electrical problem - possibly due to a loose battery connection, possibly due to a faulty aftermarket alarm. The bike kept running long after the key was turned off, and a lot of wires melted. Battery terminals melted too. I don't know if that helps identify a culprit?
 
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.
 

PitbullKC

Active Member
Might be worth checking your "run/off" switch & wire connection.

Turn your key "on", then push the "run/off" button to "run".
Your LED light on you Ignition Module should turn on for a few seconds, then go off.
IF it doesn't, check your wires from the Ignition Module back to EHC.

(FYI- I had to chase a ghost last year on my 03 Pit. Do a search for my thread, it has a TON of recommendations and info from other gracious members. I think the thread was called something like, "Okay, I give up"... lol)
 

eddie

New Member
this eddiemaxx I ride a 2004 big dog an just replace the ehc with a rip kit everything was running great I get ready to go to bike week an when I turn on key neutral switch an oil light switch an ignition module click on then off super fast
 
Top