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Headlight Modulator

Signal Dynamics Diamond Star Headlight Modulator Installation
by Bob Knowlton.

I have a Signal Dynamics headlight modulator installed on my '93 Venture and I think it is a must-have item, so I installed one yesterday on my Connie. Short of air horns and several extra headlights, nothing has more impact on cagers than a headlight modulator. Motorcycling is never risk free, but having modulators on my bikes gives me a significant and noticeable safety advantage.

For this installation, I chose to use a different method so that I didn't have to cut the existing headlight wires. This procedure is much faster and much easier. If for some reason I need to remove or temporarily disconnect the modulator, it's as easy as unplugging a few wires and then plugging the original socket back into the light bulb. A new light socket is necessary for this method of installation, but by buying the NAPA LS6235 hi temp light socket, you also get the benefit of being able to upgrade to a higher wattage bulb if you so desire without melting the stock socket. Most of the tips refer to specific wires on the modulator, so they may not make a whole lot of sense unless you have a Signal Dynamics modulator. For reference, Signal Dynamics’ original installation instructions can be found on their web.

Parts and tools needed:

  • Signal Dynamics Diamond Star Headlight Modulator with Remote Switch. I highly recommend the model with the remote switch. It makes installation and locating much easier.
  • NAPA LS6235 hi temp light socket (about $8)
  • Three 14 gauge (blue) male flat blade crimp connectors
  • One 10 gauge (yellow) male flat blade crimp connector (maybe)
  • Wire cutters, crimping tool
  • An assortment of quick connect/disconnect wire connectors. I recommend Buchanan (or similar) fully insulated blade quick connectors, available at Home Depot and auto stores.
  • Electrical tape
  • Shrink tube, if desired. Available CHEAP in bulk through JC Whitney.


  1. Remove the left side panel.
  2. Remove the gas tank. If you have enough room, you may be able to leave the tank on.
  3. Remove the left side fairing black plastic. This is the part that the left storage compartment is in. Removing it is necessary to access the horn wire, which is underneath the plastic and zip tied to a body tube. It also gives you more space to work in.
  4. Disconnect the stock socket from the light bulb.

Socket Wire Connections:

  1. The normal instructions have you cut the wires on the existing light socket. Skip that part.
  2. If desired, cover as much exposed wire with shrink tube as possible. If you don't have shrink tubing, you can cover everything with electrical tape when you're done. I'm not a fan of shortening any of the modulator wires. It's too easy to make a mistake and get one too short. Besides, there's plenty of room in the fairing to coil up the extra wire and store it. Plus, preserving the original length of the wire will allow you to install the modulator on a different bike if you ever need to.
  3. Both socket receptacles are arranged like this: As you look at the front of the socket, the top horizontal female receptacle is the low beam hot wire. The left side vertical female receptacle is the high beam hot wire. The right side vertical female receptacle is the ground wire. If you have any doubt, just check them with a voltmeter.
  4. Attach 14ga male flat blade crimp connectors to the modulator's solid red and solid blue wires. Push the blue wire blade into the low beam female receptacle on the stock socket. Push the red wire blade into the high beam female receptacle on the stock socket.
  5. Locate the ground wire on the new LS6235 socket. Wrap the LS6235 ground wire together with the modulator black wire. Install another male flat blade crimp connector to hold those two ground wires together. Because of the thickness of the two wires wrapped together, you'll probably need to use a 10ga connector instead of a 14ga connector. Insert the black wire blade into the ground female receptacle on the stock socket.
  6. Using quick connects of your choice, connect the modulator blue/white wire to the low beam wire on the LS6235 socket. Use quick connects and attach the modulator red/white wire to the high beam wire on the LS6235 socket. Socket wiring is now complete. Plug the LS6235 socket into the light bulb.

Horn Wire Connection:

  1. The Signal Dynamics modulator has a "Head's Up Alert" feature that links to the horn. When you press the horn button, the headlight will modulate for a few seconds even if the modulator is turned off. Or, if the modulator is currently active, hitting the horn button will change the modulation rate for a few seconds. This feature is terrific for getting extra attention if you think someone may not see you. With a simple modification (described below), this feature will also work at night and the impact is phenomenal. It has saved me more times than I can count.
  2. Locate the horn hot wire. It is black with a white stripe. On my 2001 Concours, the wire is in a wiring harness zip tied to the left fairing support tube. It is to the left of the triple tree, next to the left inside fairing, above the radiator. There are two plastic OEM snap connectors covered up with a black plastic protective boot. It will be necessary to cut the zip tie, push the boot back, and cut away some electrical tape to expose enough of the wire. If you want to check to make sure you've got the correct wire, insert the positive tip of a voltmeter into the slot for the wire on the OEM connector. With the bike turned on, touch the other end to a ground point on the bike or to the battery negative terminal. It should show +12 volts. When you press the horn button, the voltage should drop to 0 volts.
  3. Cut the horn hot wire (black with white stripe) a few inches away from the OEM connector. Leave yourself plenty of room and don't cut too close to the OEM connector. You'll need plenty of wire length to attach a quick connector. This is the only "invasive" cut you have to do for this installation.
  4. Locate the modulator's purple wire. Wrap the purple wire together with one end of the black/white horn wire. Put a quick connect on it. Put the corresponding quick connect on the other end of the black/white horn wire and attach the horn wire back together. The purple wire is now attached to the horn hot wire. Put the protective boot back in place and zip tie the wiring harness back to the body tube.
  5. Cap the modulator green wire. You won't be using it.

Light Sensor Modification:

  1. The Code of Federal Regulations states that headlight modulators cannot be used at night. As a result, designers must put a light sensor on the modulator that automatically shuts off the modulator during hours of darkness. Many people experience problems in properly locating the light sensor and as a result the modulator turns of prematurely on cloudy days or well before sunset. Many also abhor the idea of drilling a huge mounting hole in plastic. By accomplishing this simple and non-permanent modification, you can completely bypass the light sensor and overcome all erroneous modulator operation and mounting worries. This is a proven modification only on Signal Dynamics modulators.
  2. Gently pull the light sensor diode out of its black plastic housing. It may be held in by a little bit of RTV.
  3. Get a scrap piece of stranded 12 gauge copper wire. Pull out one little strand of wire. Wrap the little strand of wire around the exposed terminals of the light sensor diode. That will jumper the wires together and make the light sensor "think" that there's always enough light for the modulator to function. There's very little current flowing through the light sensor, so don't worry about melting the homemade jumper.
  4. Push the light sensor diode back into its black plastic housing for protection. You may need to use electrical tape to hold it firmly in the housing. Coil up the light sensor wire and store it up in the fairing with the modulator. You won't be needing it anymore.
  5. YOU are now responsible for turning the modulator off during hours of darkness. Use the main power switch to turn the modulator on during the day and off at night. You won't forget. Trust me. A constantly modulating headlight at night is more attention than you'll want. As a bonus, the "Head's Up Alert" feature will now work at night, and boy is it effective!
  6. If you don't like the results, just remove the little strand of wire from the light sensor and install the sensor per the manufacturer's directions. It's completely reversible.

Remote Switch Installation:

  1. Install the remote switch in a spot of your choice, making sure that its wires are well clear of the handlebars. I mounted mine in the same black plastic piece that holds the left fairing compartment, just below that compartment.

Finishing Touches:

  1. Wrap all exposed wire with electrical tape. Wrap electrical tape around the stock socket. That will protect it and the inserted blades from dirt and corrosion. Coil up all the wiring and store it in the fairing well clear of the handle bars. There's a nice pocket up in the fairing support tubing just to the left of the back of the headlight bulb. Use zip ties to securely fasten the wiring and modulator unit to the tubing. I don't recommend using the self stick tape that comes with the modulator. It's too much of a pain to take on and off during fairing removal.
  2. Imagining the flow of electricity helped me get everything right and may help you, too, if you're having trouble. Power comes from the stock socket and goes into the modulator on the solid blue and solid red wires. The electricity gets modulated and then is sent out to the light bulb on the blue/white and red/white wires. The horn signal for the "Head's Up Alert" feature comes in through the purple wire. When the horn is activated, the purple wire senses the corresponding drop in voltage on the horn hot wire.
  3. Signal Dynamics offers a function check chart. Also available are the DOT regulations concerning headlight modulators on motorcycles
  4. A letter to Signal Dynamics concerning the statute is also at their site.
  5. Make copies of those two documents and keep them with your bike registration in case a law enforcement officer ever has a question about the legality of headlight modulators. Their "legalness" is widely known now, so you should never have a problem.
  6. Please feel free to contact me at if you have any questions about this install. Get a modulator. You won't regret it and it might save your hide.

Article By: Bob Knowlton

December 2002 

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