Mounting a headlight modulator is an easy procedure that will help increase the visibility of your bike to oncoming traffic. Headlight modulators rapidly flash the motorcycle's headlight at 240 (plus or minus 40) cycles per minute, which attracts the attention of oncoming drivers. Headlight modulators are completely legal in all 50 states 1.
Headlight modulators are designed to increase the visibility of the motorcycle in the most critical area, the left front, to help grab the attention of oncoming traffic. The Hurt study 2 found that "the failure of motorists to detect and recognize motorcycles in traffic is the predominating cause of motorcycle accidents". The study also found that:
Types of Modulators
Headlight modulators are made by several manufacturers. Some modulate the low beam, some modulate the high beam. Some models let you choose which beam to modulate. The federal law cited above has other specifications and limitations on how they work. For example, all modulators must have an automatic system that stops the modulation at night, but still allows the headlight to function normally. Fortunately, you don't have to worry about how it works, as the modern miracle of microelectronics comes through again and makes it happen!
The Kisan P-115W-S
After careful study (see the abbreviated listing of web sites of modulator manufacturers below), I chose the Kisan P-115W-S modulator for my 1994 K75 standard. The reason I chose this model is that the standard K75 leaves very little room within the headlight cowling behind the H4 headlight to mount any other type of modulator. Most, if not all, modulators plug in to the motorcycle's headlight in place of the 3-prong plug. Some modulators need room for a small circuit board assembly somewhere near the headlight, and some are large units made for bikes with a lot of room behind the headlight. The Kisan P-115W-S is an extremely small unit, measuring only 40 mm wide and 15 mm thick. It plugs directly into the headlight, and it has a separate 3-prong plug attached to a wire cable about 2 inches long that comes off the side of the unit to insert the original headlight wiring from the bike itself. This gives enough room inside the headlight cowling for everything necessary. I had no problem at all in fitting the P-115W-S to the standard K75.
Another reason why I chose the Kisan is that it modulates the high beam. The high beam has a wider pattern than the low beam, and the high beam throws more light to the left than the low beam. This maximizes the effect of the modulated headlight to oncoming traffic, which in the U.S. is on the left side of the motorcycle. In order to be polite, you can switch to low beam when you're stopped in back of a car at a stoplight, so that the flashing high beam isn't too annoying to other drivers.
Note the small size of the Kisan P115W-S modulator (arrow)and the separate 3-prong plug (attached to red shrink wrap).
The headlight on the K75 is held on, believe it or not, by one Phillips head screw on the bottom of the chrome bezel that surrounds the headlight. Loosen the screw until the bezel is loose. The screw will not come all the way out, but be careful that the headlight itself doesn't come tumbling out of the cowling. After the screw is loose, you should be able to gently remove the headlight from the cowling.
Carefully pull off the 3-prong plug from the back of the headlight. You may have to rock it back and forth a bit, or even pry it out using a flat-bladed screwdriver, but be careful not to bend or break one of the studs. They are meant to be tight in order to ensure contact without vibrating off. There's another little light bulb (the parking light) and a ground terminal (brown wire) on the headlight. Gently pull the small light bulb out, and carefully pull the brown ground spade connector off the terminal also and set the complete headlight assembly aside. You may want to cover the headlight with something so that no dirt gets into the hole where the parking lamp was. Wrap the cable and plugs that come from the bike inside the headlight shell in a towel or plastic bag to protect them during the next step.
Now comes the scary part. In order to comply with regulations to prevent modulating at night, every modulator must have a device that prevents it from modulating when it gets dark, while still allowing the headlight to operate normally. The Kisan modulator assembly has a light sensor attached to about an 18" long wire. This sensor must be mounted through the headlight cowling and pointing up. To do this, you must drill a 10mm (or 25/64") hole in the top of the cowling! Don't worry, it's easier than you think! You need to get over the mental block of drilling into your precious baby, but I justified it by thinking if I messed up, I would simply plug the hole with a black rubber flush mount plug, and no one would notice.
Drilling holes in thin walled sheet metal is a bit tricky, as the drill has a tendency to grab the metal and stall. As an ex-machinist, I know there is a way to sharpen a drill to help prevent this from happening, but it's really not necessary for what you need to do. To help things along, you'll drill a series of pilot holes leading up to the big kahuna, the 25/64 incher.
The hole for the sensor should be dead center on top (12 o'clock position when standing in front of the bike looking at the headlight) of the headlight cowling. The sensor must be located in a way that will prevent oncoming headlights at night from allowing it to activate the modulator, so the best way to mount it is pointing straight up at the sky on top of the headlight cowling. You'll need to locate the hole fore-and-aft along the centerline of the bike, and side-to-side (or port-to-starboard!) in the middle of the top of the headlight cowling.
To locate the position for the hole, I measured back 35 mm from the front edge of the headlight cowling, which locates the hole about in the middle of the space from the front of the headlight to the beginning of the instrument module. Finding the exact center side-to-side is a bit trickier. You can eyeball it and get pretty close, or I found that you can locate the center by using your two scales. Use one scale to measure up from the Allen headed screw on one side of the cowling (they are located at the 3 o'clock and 9 o'clock positions) and then over to find the center. Repeat this from the other side until you find the spot where the distance is the same. This should be the center. It turned out that on my bike the center was located 115 mm from each screw.
Now you're ready to start drilling. First, put on your safety glasses or goggles. You must wear eye protection to do this. To start the hole, you must use a center punch to create an indentation to help locate the drill bit, otherwise you will not be able to get the drill to start without wandering. Don't use too much force, as the headlight cowling is just thin aluminum and you may put a bigger dent than you bargained for. Don't ask me why I know this! If this does happen, you can gently tap the headlight cowling from inside to straighten it out a bit.
You can't simply drill a 25/64" hole first thing. You must drill a pilot hole first to guide the bigger diameter drill. I drilled a series of holes using progressively bigger diameter drills. Start with the 1/8" bit. After you have that hole drilled, put a drop or two of oil around the hole to help lubricate the next. Drill the 1/4" hole, then the 5/16", then the drill the final hole using the 25/64". This one may want to grab the edges of the hole, so be careful. If it gets jammed, simply reverse the drill and let it back itself out. You may find that if you start the drill before touching the metal it may go smoother.
After drilling, the hole will have a burr. You must remove the burr using the round file and the emery cloth.
Now the hard part is over. Here's where my experiences in installing the modulator hopefully can help you prevent the mistake I made. The instructions that come with the Kisan modulator are not very clear on how to actually mount the sensor in the hole. I even called Kisan to ask about this, and they were very helpful, but I realized later that I still didn't understand the procedure.
The Kisan modulator comes with a small black grommet to mount the sensor in the hole. The grommet slides around the cable that holds the sensor, then fits up tight against the sensor head itself and pops into the drilled hole. The grommet is designed to keep the sensor tight and waterproof. Here's how to do it right: first pull the sensor itself up through the hole. THEN put the grommet around the sensor cable (it has a vertical slit to allow you to do this). Locate the grommet up around the threaded part of the sensor, and then push the sensor and the grommet unit down into the hole. This may seem obvious, but it wasn't to me, and the directions weren't clear to me either. Anyway, it should snap in and it will be a pretty tight fit. I had to file my hole a bit to get it to fit, and I over did it, so the fit was a tiny bit loose. I put a dab of black silicone sealant around the inside of the hole to make sure it stays waterproof. You may want to do this anyway, just as extra insurance against leakage.
Now we're getting close. Plug the Kisan modulator into the back of the headlight. Caution: only push the modulator on until it stops, don't try to force it any more after that! Replace the small light bulb and the ground terminal. Attach the original headlight 3-prong connector that comes from the bike into the 3-prong receptacle on the little extension cord that comes out of the side of the modulator. Replace the headlight assembly and attach it by tightening the screw in the bottom of the bezel. It's easy to over tighten this, so be careful or you'll strip the threads. Congratulations, you're all done! Start the bike and turn on the high beam, and after about a second the headlight will start to modulate. Life is good!
One thing to remember, you need to be in enough light so that the sensor doesn't prevent the headlight from modulating. If you flick on the high beams and the headlight doesn't modulate, you may not have enough light in your garage or wherever you're working. The sensor seems pretty sensitive, so even though I had an overhead bulb on in my garage at night while I was working, it didn't come on until I turned on another light. Try waving your hand above the sensor to see how it turns the modulator on and off.
Hope this procedure is easy to understand and helps you. If you have any questions, give me a shout at firstname.lastname@example.org.
1. Motorcycle Accident Cause Factors and Identification of Countermeasures", Volume I: Technical Report, Hurt, H.H., Ouellet, J.V. and Thom, D.R., Traffic Safety Center, University of Southern California, Los Angeles
2. U.S. Department of Transportation, National Highway Traffic Safety Administration. Federal Motor Vehicle Safety Standards 49 CFR Part 571, Docket No. 97-87; Notice 1. Executive Order 12866 (Federal Register: February 21, 1996, Volume 61, No. 35)
Other Sources for Headlight Modulators
Kriss Industries www.kriss.com