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The Two Wire Mod

52082 Views 197 Replies 28 Participants Last post by  OleDirtyDoc
Edit March 2016: So far, we know Kawi used black/red or all black for the wire running to the 10-pin JB plug from the start button. This has caused some confusion and errors applying this mod in some cases. This is probably the reason for the headlight problems later in this thread. Will try to get a couple of pics and pin locations up as soon as I can post pics again.

Edit June 2017 - Watch this video before beginning: Short video on Blue Wire & Two Wire mods

* Be aware that this mod disables the neutral start switch. Your bike will start in gear with the clutch engaged after doing this mod.*

Posting this so more people may become aware of it, recommending it as a preventative mod that could save your stator, or resolve some of the other problems it covers. The mod can also keep you from being stranded.

The Two Wire Mod

1) At the Junction Box, find the 10-pin connector (smaller of the two)

2) Locate the yellow/red stripe and black/red stripe wires (Kawi also used all black instead of black/red)

3) Remove the two wires from the 10-pin plug

4) Splice the two wires together securely and insulate properly

edit: This is the color diagram I'm using:

Link to High-Res Color Wiring Diagram: Google Drive: Sign-in

That's it!

What The Two Wire Mod Covers

1) Start Button Failure

2) Low Peak Charge Voltage

3) Charging System Brownouts - (volts dropping well below peak voltage for periods of time)

4) Charging System Failure to charge with a good stator, R/R, etc.

5) Possibly improves ignition voltage. The yellow/red branches off before the Junction Box and feeds into the IC Ignitor box. Hot and cold starting both improved on my bike.

This mod is bypassing unidentified faults and future faults with these circuits in the Junction Box.

Let us know if this works for you.

michiganteddybear did this 1 1/2 years ago for his start button.

I have the TPE/MOSFET and this mod cured charging system brownouts, low peak charge, dead start button, and hot/cold starts on my bike.

thtanner has the TPE/MOSFET that wasn't charging at all, both of ours are at 14.5v now.

Edit April 2023: Link to video for this mod.

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Those tiny letters are the ones that get fuzzy when you zoom.
I'm actually in the process of re-drawing the diagram with fresh text & colors. I may have to end up posting a mostly-done version and ask for second opinons on what some of the blobs might be.

Once the diagram is "translated" to a more readable version, it would be good to start compiling a list of known color variations by year.

I'll start a new thread on that when it gets closer. Someone with a hard-copy of the service manual can probably fill in the gaps pretty easily.
Using GIMP to edit. Typing new text and erasing the jpg lettering. I tried filters/contrast/brightness, etc, but it didn't clarify the lettering any.
In order to prevent hijacking of this mod thread, I'm posting the Color Wiring Diagram thread.

First draft is HERE.

Any input and/or corrections from the manual will make for a better finished product!
yellow/red in the back row, second pin from the bottom
black/red in the front row, bottom pin
Isn't the yellow/red in the front row too? Pin 13 to starter relay's coil?
Not on my plug, those two middle pins are empty.
That's crazy! If you never had anything on pin 13 (front middle on 10 pin connector), how did your starter ever work? What pin does your yellow wire from the stator connect to?

Is your JB stock 2003? Is it even remotely possible theres more than one JB design?
Same part number from '86 to '06. I'm tempted to pop one apart and see what's going on internally.
If you squint you can see the pins and traces on the board in this video:
The yellow wire that I have going in to pin 9 (10 pin connector, second up on back row) is what triggers the headlight relay. If you did the headlight relay bypass mod, you would not NEED a wire there, and it might just look like what you're expecting the yellow/red wire for the 2 wire mod to look like, with the yellow/red plug having fallen out from pin 13 (third pin on front row, out to starter relay) on the road somewhere?
Just to satisfy my curiosity, what pin position was the yellow stator stub in? There's a cascading pin position difference, and I just wonder where the discrepancies end.

You had no wire at my yellow/red position.
your yellow/red wire was attached to my yellow position.
your yellow wire is attached to my ? position.
your ? wire is attached ... etc.

Caleb mentioned a picture you posted of your 10 pin connector, but I must have missed it.
Found the pictures. Thanks!

So I went ahead and connected my yellow/red and black/red wires (which were connected at pin 13, front middle position, and pin 11, front row bottom position).
Starter worked just fine. I didn't check to see if it would start in gear. ;)

Anyway, that leads me to believe that the wiring diagrams are right, in as much as they have the correct pins labelled. Wire colors can deviate, obviously (my pin 11 is red and black, but the diagram lists black).

What I can't wrap my head around is how your yellow/red wire, which MUST be going to the starter relay if its spliced to your black/red, could have been connected to the stator-in pin when it came from the factory. It just doesn't make sense.

By the way, I was able to pull the pins without cutting the wires by pushing a very small flathead screwdriver into the edge of the pin hole on the connector which allowed me to put everything back to stock after testing. Might help someone down the line who doesn't want to cut their harness.
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The pinouts are listed on the JB schematic from the service manual, page 298. Using the pinout labels there and tracing out the circuits, I was able to match the pinouts to the wire colors. Took a while.

I understand that your yellow/red was never connected to the stator, but it is currently stubbed at the "from the stator" pin on your junction box, used to trigger the headlight. I don't think it ever would have gotten voltage there, which is what confuses me so much, and why I keep poking at the mystery. The yellow stator wire (now missing on yours) should have been connected to pin 9 from the factory, not the yellow/red. I would have said that your wires just got switched while bypassing relays, but MTB's yellow/red was connected to the same JB pin. Was that possibly a mutual mis-step in the early days of the mod? I'm at a loss.

I haven't installed a digital meter to my dash, so I can't really get a useful voltage reading.

I realize I'm vulnerable to a relay failure, but if it fails I can just do the mod then, even in a parking lot to get me rolling, if need be. No biggie.
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It seems to me that the unregulated stator lead driving the headlight relay is more of a hazard than the interlock when it comes to burning stuff out. I'm trying to figure out just what exactly I want to do with that ... the standard relay bypass seems worth doing, but I sort of want to move the headlight wiring so it is controlled on just a manual toggle switch when the bike is on. Still haven't settled on what I want to do.
Also - something I've been unclear on. With the stock system, the headlight relay becomes engaged when the stator output reaches the junction box. However, it stays on until the key is turned to the off position even if the engine isn't running. What causes that?
The stator triggers the initial turning on of the headlight, meaning the light won't come on until the engine is actually running, providing as much current to the starter motor as possible.

The output of the switched current is looped back to the input of the relay coil, so once the headlight comes on, the output of the relay's switched current 'latches' the relay closed. When the key is turned off, the latching voltage that passes through the switched legs to the coil is removed, and the relay resets.

I would prefer to find a "normally closed" relay and connect the starter button to its coil so the headlight is 'always on' without having constant current through the coil, but the headlight would turn off when you crank the engine.
Couldn't you use the normally closed output on any generic 5 pin relay to disengage the headlight? Sounds like you and I are describing two versions of the same solution.
Yup. same result, just one less pin. ;) Being fairly new to automotive electronics, I don't know what's easily available. I did a brief search for 4 pin relays and only found large-scale suppliers, so if a 5 pin is easier to come by, it sounds like just the thing.
That's perfect, caleb, thanks for the link. I'll order some immediately.
Does the mod void the sensor in the clutch lever? Just accidentally broke that little bugger....
After the mod the bike will start while in gear with the clutch lever released.
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What would cause my 98 rpms to jump up before I release the clutch
Best start a new thread for your question since it is unrelated to the two wire mod, and you'll be able to get more help. **EDIT** Just saw that you opened one. Thanks.
No, the mod would be putting the two wires together, this worked for cutting out the clutch sensor and neutral starting, but cut out my headlight. It was mentioned earlier in this post that someone spliced the two together and ran them into the junction box where the yellow red wire was. This allows me to start in gear clutch out, but still have a headlight
Just checked the schematic, and Jb87 is absolutely right. On a stock bike, splicing black and yellow/red together without reconnecting to pin 13 of the junction box robs the headlight relay of it's path to neutral for the primary/coil. Doing the blue wire mod (bypassing the headlight relay, thus removing pin 13 from the headlight circuitry) would be an alternative to reconnecting to pin 13.
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Just for the record, here's the original "reconnect to pin 13" post

Ok so I did this mod on my 95 vulcan because I am teaching my wife to ride and I could not have it not start on her at a corner if it stalled. My wiring is ALL stock there have been no wiring mods.I cut the wires but did it a little way back from the plug (Maybe an inch) I twisted the 2 wires together and it worked.
My head light like the other fella reported did not work. So I did the simplest thing I could think of I Hooked the wires back up the way they were 1 at a time to see what would happen.
Black with red stripe hooked up = still no head light
Yellow with red stripe hooked back up = Head light

So decided to see what would happen if I just spliced the black with red stripe wire into the yellow with red stripe wire with the yellow and red striped wire still plugged in to the harness and connected to itself.
Here is the result
My neutral safety switch is bypassed the bike will try to start in gear if button is pushed and I have a head light.

So trusting myself I have soldered the connection and sealed it up.
The pig tail from the black with red stripe wire I just sealed up and left.
Hoping this helps someone else or if I am way off base let me know I know nothing about the wiring of these bikes I just kind of thought it out.
Good work, Jb87 digging that back up.

Spockster, can that be added to the 1st post so the next batch of modders have all the info they need? Your memory sure looks impressive compared to mine. ;)
If the junction box is unchanged across all years (which it seems to be), then when modding a stock harness, pin 13 must always be attached to the early years' black or later years' black/red wire in order for the headlight to work. The color of the wire looks to be the only change there.

The only major divergence would be the non-US version which doesn't use the headlight relay at all, so pin 13 could be disconnected as part of the mod.

I'm guessing that those who DIDN'T have headlight issues when doing the two wire mod had already bypassed the headlight relay. Is there any evidence to the contrary? If so I'll try to dig deeper.

I would think that just mentioning that the wire could be black or black/red would be enough without trying to find two wiring diagrams. There are no other similar wires on that connector, so it should be fairly obvious to follow.
I thought the results were mixed, but those with no headlight problems also had later model bikes. Have not gone back to review.

Mine already had the headlight bypass in place when I did the two-wire mod.
You could just pop the blue wire back over to pin 8 on your bike and see if you lose your headlight... >:)
Do you have a photo of this?
Do I splice the two wires together, and then still put the jumpers on the pins?
Do not jump the pins after cutting the wires.

BUT if you cut the yellow/red wire you will also have to do the blue-wire mod in order to get your headlight to work.

If your headlight works after cutting WITHOUT doing the blue-wire mod, please let us know.


Just for kicks, the alternative would be to cut the black wire, cap the stub and splice the long end to the yellow/red without cutting or removing the yellow/red from the connector. This would eliminate the need for the blue-wire mod.
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