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The Two Wire Mod

52085 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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Sticky Sticky Sticky Sticky Sticky Sticky Sticky Sticky
x2 sticky... .. and thanky ODD.
MTB, I wouldn't have known about the voltage changes without the dash mounted volt meter. Might never would have connected the increase in volts with doing this mod, I also just needed the start button working again.

Thanks for the quick sticky.

Spread the word folks, I think this will help a lot of riders. I'd say it ranks somewhere on the list of things to do when you first bring your Vulcan home, because it could prevent ever having these problems. On the list with checking spline lube, etc. Add to The Verses?

Don't know who might have discovered this bypass first, but I figured it out for myself and as soon as I mentioned it, MTB confirmed it worked for him 1 1/2 years earlier. I then knew to proceed with cutting those wires. Thanks again, MTB.

If anyone sees a mistake in the write-up, or comes up with more info, we'll edit it into the first post as well. Wasn't sure what to call it, JBStarChargVI or JBSCVI (junction box start charge volts ignition) seemed too much, The Two Wire Mod sounds simple, as it is to do.

It's possible this mod might make the ign. coil relay mod obsolete. That yellow/red shorting in the JB, may be responsible for the voltage drop through the yellow/red to the IC and then to the coils. Or the improved voltage on the yellow/red at the IC provides better spark timing adjustment on cranking. I'm just not sure.
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KC2 has repaired some JBs, he may have something to add if he sees this. Haven't seen him for a few weeks though.
So I did this mod and now my headlight doesn't come on. No low beam or high beam and no warning lights on the dash. I'm know my light was working yesterday. My bike is stock otherwise, can someone help me?
You may have uncovered some info we need for doing this mod.

On mine, I already had the blue-wire headlight relay bypass in place, so I had no trouble with the headlight. Not sure how MTB or tanner has theirs set up.

You may need to move the blue wire for this mod to work. We'll see.

Meanwhile, verify that you got the correct pair of wires off the 10-pin plug. Make sure you didn't cut the solid yellow wire that triggers the headlight relay.
Also be sure you used the 10-pin for the The Two Wire Mod and not the 8-pin, the plugs have both colors on them.

Correction: The headlight bypass moves the blue wire on the 8-pin plug, and moves it to the empty slot on that same connector. (empty slot is directly beside the blue wire)

You need to release the locking tab on the spade with a stiff wire or pin. It will lock into the hole when you push it back in.

There's more info and a video on this thread:

Correction: The headlight bypass moves the blue wire on the 8-pin plug, and moves it to the empty slot on that same connector. - 8 pin - (empty slot is directly beside the blue wire)

Correction: The headlight bypass moves the blue wire on the 8-pin plug, and moves it to the empty slot on that same connector - 8 pin -. (empty slot is directly beside the blue wire)

You do not move the blue wire to the 10-pin.

What year is your bike, first time? Baffled why this didn't work on yours. Are you able to post any pictures of the wires in question?

To answer your question, the 10-pin comes out the same as the 8-pin. The plugs just get stuck tight. Have to release the lock and wiggle the plug.
I won't try to change your mind. But did you splice the wires together on the plug, or off the plug?

Did you see the info about the blue wire mod? It does not involve the 10-pin plug.
Sounds like you did it right, still baffled why it affected your light.
I still don't know if the headlight bypass was done right.
Thank you again, Spockster.
Hey, you're welcome, and those balancer bushings should be almost there, maybe today.

If you don't use them right away, you might put some fresh motor oil on them and keep them in the bag. Gave them a shot of FRP when I mailed them, the FRP might take the motor oil off them, even though it's oily itself.
Please excuse my ignorance, but what is FRP?? :confused:
Foaming Rust Penetrant - FRP

When they closed the power plant, they were giving it away like candy. Think I'm down to my last can. :( Can't buy it anywhere. It's really good stuff.
Was tempted to say this was a difference in older bikes, but tanner has an '89 and a '90 listed. Not sure if he has a newer one that he was working on. I know when he swapped in a harness, there were fewer wires than it had originally, but the Two Wire mod worked after that.

Not sure you're getting the benefits with the yellow/red still tied to the JB, but still don't know why two bikes have had the headlight problem.
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

It's the smaller plug, 10-pin, so the bottom plug. Or just count the holes, including empty holes.

If the spades are corroded from the battery acid, that can be a problem and they need cleaned/tightened..

My wiring diagram showed the yellow/red changing colors at the plug under the fork neck. My bike (2003) has the yellow/red continuing all the way to the Junction Box from the start button.

So there seems to be variations with different diagrams.
Some WD40 might slicken it up.
Some sort of spray lube should help if there's corrosion from battery acid. Mine was clean but still stuck, just plastic to plastic. I used a larger screwdriver blade to get it moving. But the plastic wasn't rotten either. It wasn't easy pulling the plugs even after being removed once.

The black/red comes from the start button. When you hit start, current from the start button trips the relay in the JB, current then from the yellow/red triggers the starter solenoid under the right sidecover, starter turns, happy noises occur, and away we go..

Going back toward the handlebars.... Black/red comes from the start button, through the connector under the tank, and back to the JB. It is this wire on my bike that was the same color all the way to the JB, but the wiring diagram showed it changing color (black/red to black) at those plugs under the tank, so my color diagram was incorrect.

This black/red also has a yellow/red wire that branches off before the JB, and runs to the IC Ignitor (CDI) and is labeled "start". We speculate this wire may cause the IC Ignitor to alter timing on engine cranking, but we are really unsure of it's function.

Because of that branching wire to the IC Ign., and the improved starting I observed after the Two-Wire Mod, I'm thinking the mod may have improved ignition volts during cranking. (same as the coil relay mod)

I've added the color wiring diagram to the first post, and here. Save to your device and zoom in.

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So it seems to me that a lot of these electrical mods bypass crap relays in the JB. Has anyone found a replacement for these or some other way to resolve? I wonder if there is a decent JB from a different bike that could be subbed for ours. I just want my bike to work for spring and these electrical issues seem to be the biggest draw back to the VN750. Maybe I'll buy one on ebay and see if I cant just make a circuit card that works by hand..
This mod bypasses the starter relay in the JB, which is redundant and prone to failure. Kawi used a relay to trigger a relay (starter solenoid). Starter circuits have been fine for decades with just the one relay.

Some have repaired JBs, but in this case it's simpler to just bypass, and the other possible benefits are a bonus.
Ahhh Gotcha Any idea what wire is supposed to be the black/R on the 1986 harness? I know everyone says to just use the one in the same slot on the connector but that's not quite solid enough advice for me
From looking at one of the pics you posted in another thread, the wire in that position looks white or lt.gray? Lt. blue?

I would go to the plugs under the left side neck cover and see if that wire is there. May be necessary to trace completely back to one side of the start button to confirm. If needed I would check continuity from the JB plug to where it is found up front or do that in reverse, find the start button wire at the JB plug.

Have to find the correct plug up front, right now I don't recall which plug carries the start button.
If youre talking about the wire at the top of the picture, over the black one, Thats actually white haha. Grease and filth is an extra custom mod the PO added free of charge.. Starngely enough there was also a VN750.com grill cover on the bike as well
You may get lucky and find there's only one white wire in the set of plugs up front. I would still verify that the white runs to the start button. The white wire could possibly change to another color at the neck cover plug. The diagram shows that happening, but it wasn't that way on my bike, it has one color all the way back.

You're sort of the guinea pig on this one. If you are successful, you'll probably be solving the headlight issue posted earlier. May need to edit in two pics, that one of yours and one with the black/red on the 10-pin plug.

So I'm wondering where the early wiring diagram is? That wire didn't turn colors with age! ;)
Yellow/red goes directly from the junction box to the starter relay with no branching. Black branches onto Red/White for the connection to the Igniter.
There is a yellow/red that runs to the starter solenoid from the JB.

But the diagram also shows a yellow/red branching from the black (my black/red) and running to the IC Ignitor. It's about in the middle of the diagram.

Have never seen where this wire actually branches in the harness, but it is present on the IC Ign.
I do recall someone posting about a spliced wire in the middle of the harness.

The wire codes are really fuzzy in the color diagram, right now it looks like the branching IC wire could be red/white instead of yellow/red.
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