Have you ever seen those motorcycles coming at you with those headlight modulators? The pulsating headlight makes them very noticeable to other motorists. Unfortunately, these units can be rather expensive. After doing some research, I've come up with an inexpensive way of replicating these headlight modulators.

We'll need a couple of components for our project. We're going to use a Grote electronic flasher, part number 44530, to handle the headlight pulsation. We'll also be using a 30 Amp double-pole relay, Standard Motor Products part number RY48 (or NAPA PN# AR204).




Other parts include a little bit of wire (14 or 16 gage, less than a foot in length) and several insulated female spade terminals. As far as tools are concerned, you'll need a Philips screwdriver, a jeweler's flathead screwdriver (about 1/8" wide) and a pair of wire cutters/crimpers.

I've come up with two different versions of how to hook this circuit up. One way has the headlight's high beam oscillating when the headlight dimmer switch is flipped to high beam. We'll call this Option One. The other has the headlight's high beam oscillating when the headlight dimmer switch is flipped to low beam. We'll call this Option Two.

Before we begin, let's familiarize ourselves with the connections on both the relay and the flasher unit.

The Relay


The relay will have five spade terminals sticking out of it. Two of the five terminals are hooked to an electromagnetic coil inside the relay and they are marked 85 and 86. Terminal 85 is the power-in terminal and terminal 86 will be hooked to ground completing the circuit. The other three terminals (terminals 30, 87, and 87a) are for a double-pole switch. The term "double-pole switch" tells us that the switch has the possibility of sending power down one of two legs depending on its state. Our relay has two states: energized or not. The "not energized" state will have terminals 30 and 87a connected in a normally closed (nc) position, allowing power to flow across them. Terminals 30 and 87 are said to be normally open (no) in this state, i.e. no power will flow across those terminals. The "energized" state is when the coil has been powered up on terminal 85 and the relay's electromagnetic coil pulls the switch closed across terminals 30 and 87. Now terminal 87 is closed and terminal 87a is open. As soon as power is removed from terminal 85, a spring pushes the switch back to its "normal" state, closing across terminals 30 and 87a. Notice that terminal 30 is a common terminal to both states. Therefore, terminal 30 is usually referred to as the "common".

The Flasher



When you look at the electronic flasher, you will see an 'X' and an 'L' stamped on the unit. Power coming into the unit should be hooked to the 'X' terminal and the headlight high beam should be hooked to the 'L' terminal.

We will also need to adjust the flasher's rate of oscillation. You will need to carefully remove the plastic cover from the electronic flasher unit by gently prying out on the retainer clips on either side of the cover. Once the cover is removed, you will see a pot on the circuit board next to the capacitor. The pot has a small square hole in it that is adjustable. Using a small screwdriver, turn it clockwise to increase the flash rate or counterclockwise to decrease it.


I recommend doing this before building your harness as things get pretty tight afterwards. A couple of jumper wires will work to temporarily hook up the headlight and flasher unit. You'll need to hook one jumper wire to the yellow wire coming from the dimmer switch to the 'X' terminal on the flasher. Then hook another jumper wire to the 'L' terminal on the flasher unit to the yellow wire of the headlight harness. Lastly, you'll need another jumper wire hooked to the black wire of the headlight harness to ground to complete the circuit.

After securing the headlight so it doesn't fall and break, start the bike and turn on the high beam. Slowly turn the pot until the highbeam oscillates on and off at a decent rate. If you turn it too much, the high beam will not fully light and will diminish the effect. Once you have it set to where you like it, replace the cover. (WARNING: Be carefull where you grab the flasher's printed circuit board. The capacitor can give you a nasty jolt if you touch its terminials.)

Here are the steps...
1. Remove the headlight from the headlight bucket by removing the two screws from the bucket. They are located at the 4 o'clock and 8 o'clock positions.
2. Unplug the headlight from the wiring harness and set it aside for now.
3. Unplug the headlight harness from the dimmer switch wiring harness.
4. See the instructions under the flasher unit section for adjusting the flasher frequency. Adjust flasher unit.



5. Cut the headlight harness approximately in half.
6. Remove any plastic wire protector tubes from the harness and discard.
7. Determine which option you will be installing on your bike. Option One will preserve the low beam, while Option Two will preserve the high beam.
8. Go to that section to complete the install.

Option One (Preserves Low Beam)



Here's the wiring diagram I've come up with for oscillating the high beam when the headlight dimmer switch is in the 'High' position. This is how it works: power flows to the normally closed side of the relay contacts, terminal 87a, through to terminal 30. From there, power continues on to the low beam filament of the headlight. At the same time, power flows to the flasher unit, then on to the high beam filament of the headlight. The flasher unit causes the high beam filament to oscillate on and off rapidly.

To disable the headlight modulation feature, flip the headlight dimmer switch to the 'Low' position. Power then flows to the relay's coil terminal 85 energizing it (terminal 86 being grounded). At that point, the switch inside the relay closes across terminals 87 and 30. Power then flows from terminal 87 through 30 out to the low beam filament.



9. Using your wire strippers, strip the insulation off all the headlight wiring harness wire ends.
10. Twist together both the bare black wire ends and crimp on an insulated female spade terminal.
11. Plug this newly crimped female spade terminal onto the relay's terminal 86.
12. Twist together the bare green wire end coming from the headlight wiring harness's dimmer switch circuit (white plug-end) and a short piece of new wire (stripped of course) and crimp on an insulated female spade terminal.
13. Plug this newly crimped female spade terminal onto the relay's terminal 87.
14. Crimp on an insulated female spade terminal on this new wire.
15. Plug this newly crimped female spade terminal onto the relay's terminal 85.
16. Crimp on an insulated female spade terminal on the bare green wire coming from the headlight wiring harness's headlight end (black plug-end).
17. Plug this newly crimped female spade terminal onto the relay's terminal 30.
18. Twist together the bare yellow wire end coming from the headlight wiring harness's dimmer switch circuit (white plug-end) and a short piece of new wire and crimp on an insulated female spade terminal.
19. Plug this newly crimped female spade terminal onto the relay's terminal 87a.
20. Crimp on an insulated female spade terminal on this new wire.
21. Plug this newly crimped female spade terminal onto the flasher's terminal 'X'.
22. Crimp on an insulated female spade terminal on the bare yellow wire coming from the headlight wiring harness's headlight end (black plug-end).
23. Plug this newly crimped female spade terminal onto the flasher's terminal 'L'.
24. Go to step 25.

Option Two (Preserves High Beam)



On the low beam side, power flows in from the dimmer switch to the low beam filament and to the flasher unit. From the flasher, it flows threw the normally closed (terminals 87a and 30) relay on to the high beam filament. The flasher causes the high beam filament to strobe.

When the dimmer is flipped to high, the power flows into the coil of the relay (terminal 85) which pulls the contacts closed across terminals 87 and 30. This allows the power to flow from the high beam circuit threw to the high beam filament. Since there's no flasher involved, it remains constant, i.e. a normal high beam.



9. Using your wire strippers, strip the insulation off all the headlight wiring harness wire ends.
10. Twist together both the bare black wire ends and crimp on an insulated female spade terminal.
11. Plug this newly crimped female spade terminal onto the relay's terminal 86.
12. Twist together the bare yellow wire end coming from the headlight wiring harness's dimmer switch circuit (white plug-end) and a short piece of new wire (stripped of course) and crimp on an insulated female spade terminal.
13. Plug this newly crimped female spade terminal onto the relay's terminal 85.
14. Crimp on an insulated female spade terminal on this new wire.
15. Plug this newly crimped female spade terminal onto the relay's terminal 87.
16. Crimp on an insulated female spade terminal on the bare yellow wire coming from the headlight wiring harness's headlight end (black plug-end).
17. Plug this newly crimped female spade terminal onto the relay's terminal 30.
18. Twist together the bare green wire end coming from the headlight wiring harness's dimmer switch circuit (white plug-end) and the bare green wire coming from the headlight wiring harness's headlight end (black plug-end) and crimp on an insulated female spade terminal.
19. Plug this newly crimped female spade terminal onto the flasher's terminal 'X'.
20. Crimp on an insulated female spade terminal on a short piece of new wire.
21. Plug this newly crimped female spade terminal onto the flasher's terminal 'L'.
22. Crimp on an insulated female spade terminal on this new wire.
23. Plug this newly crimped female spade terminal onto the relay's terminal 87a.
24. Go to step 25.

Finishing Up
25. Carefully reposition the existing wires in the headlight bucket so that you have room for the relay and the flasher unit.
26. Plug the headlight wiring harness into the headlight dimmer switch harness (white plug-end).
27. Plug the headlight into headlight harness.
28. Reinstall the headlight, making sure not to damage the wires, connections, or components inside the headlight bucket.
29. Reinstall the headlight bezel retaining screws.
That's it! You're done.

In closing, here's a little video of the working prototype on my bike. In the video, you'll see me switching the headlight dimmer switch from 'Low' to 'High'. Note the strobing of the headlight after I've flipped the switch.