VTX 1800C Diode Fix

Posted by Bare | Last Updated January 20, 2011

These are directions for installing a “diode kit” on a VTX 1800C model. This kit is available from Kuryakyn (part #4709) for about $6 or I have details on how to build your own with parts from Radio Shack. The diode kit cures problems inherent in the C model regarding LED blinkers. Let me apologize now, this write up was done long after I’d added my own diode kit in an effort to help others having problems, so this article is not as thorough as many others I’ve done. I just couldn’t see tearing my wire harness open again to snap pictures.

This project affects parts of the electrical system on your bike so if you should decide to undertake this task you will need the tools and know-how to solder wires together and seal them with heat shrink and/or electrical tape. If you are unsure of what you are doing this project could result in damage to your bike’s electrical system. Any similar work performed on your vehicle is done at your own risk. With that said, this is not a very difficult task if you have basic electronics skills. You just need to be careful and take your time.

Now, you may be wondering – why do I need a diode on my 1800C when I change to LED blinkers?

To understand and explain this thoroughly I think a schematic of the 1800 C’s turn signal setup will help (see inset).

Turn signal schematic

What makes the C model different from other VTX models is that it has only one indicator light on the dash to let you know the blinker is on. Every other VTX model, 1300 and 1800, has 2 dash lights – one for each side – thus eliminating the cause of the problem on the 1800C.

To better understand this you first need to understand how a basic DC (direct current) electrical circuit works. Take for example just the right hand side of the schematic above, disregarding the indicator light. Power comes from the 12V supply (your battery) through a 10A fuse which is designed to protect the circuit if there is a “short” in it. It then goes past the fuse to the relay which determines the rate at which the signal flashes, and then to the switch which is what actually turns the circuit on and off. With the switch in the “on” position (in the schematic it is “off”) the circuit is completed and power is allowed to flow from the battery, through the fuse, relay, switch and into the “load” (the blinker bulbs in this case) and then finally to ground.

The important thing to learn from this is that in order for any circuit to function it needs to be complete from 12V all the way to ground. The switch in this circuit is what allows power to flow and the blinkers to blink.

With this basic understanding of how circuits work it will help to understand how this one indicator light functions. By having only one indicator light you can see that it must get power from either the left or right side in order to blink. The problem is that Honda designed this system in such a way that when the left blinker goes on it provides power to the indicator light which then finds its electronic ground (to complete the circuit) through the right side of the circuit – and vice-versa for the right blinker. If that confuses you then look at the diagram above and cover up everything on the right side. With the switch flipped to the left the right side of the circuit doesn’t function BUT the indicator light uses it as a way to find its ground so it can light up.

Once you understand how the indicator light gets its power from each side of the circuit then you can see how a small amount of power is “leaking” over from one side to the other. This small “leak” doesn’t matter when you have the stock incandescent bulbs or even aftermarket halogens because they require more power to light up than the little indicator light can “leak” to them. LED signals on the other hand only require very small amounts of power to light up and the indicator light DOES leak enough power to light these. So instead of hitting the left blinker button and getting a left blinker, you get “emergency flashers” with all 4 lights blinking together.

Diode schematic

So therein lies the problem – how do you get the indicator light to still function with LED signals based on the design of Honda’s circuit? The answer is to modify the circuit – like the picture on the right. This schematic shows how to rewire the indicator light portion of the circuit. Using a diode kit or diodes from Radio Shack to fix the circuit so that no “feedback” can occur from one side to the other. The section of the circuit inside the dashed box represents the diodes you’re adding to the circuit.

To better understand diodes, think of them as a one-way valve for electricity. They let power through in one direction only,.In this case it lets power get to the indicator light but the power cannot flow back behind the diodes.

Required tools/Materials

  • 5mm allen
  • Wire cutters
  • Wire strippers
  • Philips head screwdriver
  • Soldering iron & solder
  • Electrical tape or heat shrink tubing
  • Kuryakyn #4709 (diode kit) or Radio Shack #276-1143 (two 3A diodes)

Removing the dash

5mm dash screws

To start, you’ll need to get to the wire harness that runs under your dash panel for all the warning lights. Remove the dash panel by removing the three 5mm screws closest to the seat (see pic). Be careful not to lose the almost invisible nylon washers that come off with these screws. Once the screws are out you’ll have to take off your gas cap to pull the dash off.

NOTE: Leave the gas cap on until you get all the screws out and away from the dash – this way you ensure you do not drop the screws IN the gas tank!

With the gas cap removed, slide the dash forward to get it off of the little tab it sits on at the front of the tank. Make sure you do not lose the little rubber cover that sits on this tab, it helps prevents your dash panel from rattling.

With the dash panel removed from the tank remove these two 5mm screws:

Light cluster screws

Then flip the dash panel over and remove this one here with a philips screwdriver:

Rear light cluster screw

Removing the “light box” from the dash panel makes working on this much easier and eliminates any chances of damaging the chrome finish on the dash.

Wiring the diode

Dash light wire harness

Now that you’ve got the dash off you can concentrate on the wiring. There will be electrical tape wrapped around the harness to hold the black sheath on. Peel it back (I don’t recommend cutting it off because of the wires!) and slide back the black plastic sheathing on the wire harness.

By pulling back the sheathing you can get to the wires you need and still have enough room to work with them – plus when you are done you can slide the sheathing right back over the wires and it will look like nothing was done. I found it very helpful to use a spring clamp (like a giant clothespin) to hold the sheathing out of the way once it is pulled back.

With the wires accessible find the green, orange and light blue wires in the harness and separate them from the others so you can work with them. Next, you’ll need to cut the orange and light blue wires making sure to leave enough slack to work with on both sides of the cut.

Read this part carefully…
With the orange and light blue wires cut, strip the insulation from the orange wire coming FROM the dash lights and splice it into the green wire in the harness. This green wire is your bike’s ground and you want to tap this wire into that ground. Once you solder the orange wire into the green, heat shrink the connection or wrap it tightly with electrical tape.

Now you have 3 wires left, 2 coming from the bike (orange and light blue) and the light blue wire coming from the dash lights. You have to decide whether you are using the Kuryakyn premade diode kit or if you are making your own kit from the Radio Shack diodes.


Kuryakyn diode kit wiring schematic

Kuryakyn diode kit
The Kuryakyn diode kit has 1 blue wire and 2 red wires. You want to solder and heat shrink the 2 red wires from the diode to the orange and light blue wire coming from the bike. When you’ve completed this step, you will have one orange wire coming from the bike soldered/heat shrunk to a red lead from the diode and one blue wire coming from the bike soldered/heat shrunk to the other red lead from the diode. Once this is done you only have the blue wire from the diode and light blue wire coming from the dash lights. Solder/heat shrink these 2 wires together and you are done.

When you are finished you should have a circuit just like the pic on the left.

Now you can skip this next section and go down to “Finishing Up“.


Radio Shack diodes

Diode schematic

If you bought the diodes from Radio Shack then you have a little prep work before you can install the diode setup. What you’re going to do with the Radio Shack diodes is build what Kuryakyn sells you for several times the price. Take the 2 diodes included in the package from Radio Shack and find the stripe on them. Put both stripes pointing in the same direction with both diodes side by side and twist the leads on the striped end together. Take these now connected leads and solder them to the light blue wire coming from the dash panel. With that completed, you have the 2 opposite ends of the diodes which are currently not connected. Solder one of these to the orange wire and the other to the light blue wire. Be sure and heat shrink or electrical tape these connections well. You don’t want any of these leads shorting out against each other.

When you are finished you should have a circuit just like this picture.

Finishing up
At this point it would be wise to test your blinkers to make sure they work properly. If they work, then you just need to clean up the wire harness – make sure all your connections are solid and well-sealed, then slide the black plastic sheathing back over the entire harness. If they do not work then retrace the steps and check all your connections. Wrap a little electrical tape around the end of the sheath just like what you took off when you started. Then reverse the steps above to put your dash back together and on the bike.

I want to mention that this is not strictly a problem with the VTX 1800C model. I have seen this same problem on other Honda motorcycles that have a single signal indicator on the dash. So if you have a friend who just replaced his blinkers with LED’s and has a single dash light with this problem – consider looking into these diodes as a solution.

9 Responses to “VTX 1800C Diode Fix”

  1. ken says:

    thanks a heap for the time and effort you put in creating this page. I had this problem and it had me stuffed for ages untill I found this. love your work. ken , Gold Coast Australia

  2. Hey: GRE8T job on the VTX 1800C turn signal wiring diagram. I’ve been looking for this for a long time. Been messing with LED’s and incondenscent add on lights to my VTX and fried my LED flasher. Got a new one from Dennis Kirk, and it was only marked G….L….P….{+}…Now I had figured out that G was for GROUND on the Honda, but what was Power {+} and what was T/S Main wire. Had a white and a gray coming from the bikes harness, and your drawing told me exactly where to put my leads. THANK YOU…one thing I would like to see…is what color is the POWER {+} wire coming from the bike….hopefully it’s WHITW with black markers. Regards Elmer W. Ingram, Jr.

  3. elcubanito says:

    I also had the same problem an doing this mod was a piece of cake that fixed the problem of bleed power over

  4. April says:

    Just wanted to say thanks for such a well written piece!

  5. [...] best description I’ve seen on this issue and its solution is an article entitled “VTX 1800C Diode Fix” on the “Bareass Choppers” (you read that right!) website. Read the article [...]

  6. HatfieldJim says:

    Great instructions for a great fix

  7. Troy says:

    This was great. I worked on my bike for two days before finding this article. I had the led lights working and my bike on the road in hour after reading this article. Thanks for the help

  8. Horseshoer Mat says:

    Realllllllllly helped! I have a 1957 beetle converted to a meyers manx, I just redid the dash, speedometer and indicator signals. I ran into this same problem and the radio shack setup is the one for me. Thank you for the great write up.

  9. lee peoviack says:

    great fix did the radio shack version cost me 1.99

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