Headlight relay harness for Honda NT650 Hawk GT

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Before     After

If you've ridden a Hawk at night you've probably noticed that the headlight leaves something to be desired. 

I'm making and selling a suplementary headlight wiring harness that uses marine grade high gauge wire, and automotive relays to aleviate this shorcoming.

Answers to questions

• What causes the light to suck?
• Why shouldn't I just use a high-wattage bulb?
• What do I get with the kit?
• What are the options?
• I've got an aftermarket fairing with a funky headlight, can you still help?
• What about my CBRGSXRYZF 600 or my '72 Bultaco?
• How much does it cost?
• How do I order one?
• Is installation hard?
• Do I have to worry about power consumption?
• Show me how good it is! (testimonials)
• Can I see some before and after pics?

What causes the light to suck?

• older lens and reflector design
• deficient wiring

The wiring is deficient for several reasons,

• small gauge wire
• too much of it
• too many switches

In the case of the Hawk the power has to go from the battery, through the main fuse, through the ignition switch, through the main fuse box, through the right hand side starter switch (the headlight turns off when you press the starter) across to the left side high/low beam switch, and then finally to the headlight.  All of the wiring is pretty small gauge, (18 I think) and each of the switches adds resistance.

When I did my measurements I measured 9.6 volts across the headlight with the headlight on, but not the engine, as compared to 12.8 volts at the battery.  When I hooked the bulb directly to the battery using big wire the voltage was 11.9 volts.

That 2.3 volts makes a significant difference in the amount of light put out by the bulb, as the relationship between power and brightness is not linear, a properly powered 100 watt bulb puts out noticably more light than two 50 watt bulbs.

Why shouldn't I just use a high-wattage bulb?

Some people will just use a high wattage bulb in the stock harness to get some more light.  This works, sort of, but it's not a good idea.  Here's why:

• The resistance of the stock wiring will not get you the brightness you expect, as the voltage drop will be more apparent with a higher wattage bulb.
• The added load on the stock wiring will generate heat in all the switches, potentially melting them.  This doesn't happen very often, but if it does you've got a lot of work on your hands replacing them, and it's likely to be expensive.
• When you open a switch that has current going through it there is a spark.  The spark damages the contact points of the switch.  The size of the spark and the damage caused is proportional to the amount of power going through the switch.  The switches will fail sooner than they would otherwise.  The relays are designed for high load, and are easily replacible in the very rare circumstance that they fail.  They're made by Bosch, so failure is unlikely.
• Read this testimonial. 

What do I get with the kit?

What this harness supplies is some marine grade large gauge wire from the battery directly to the headlight, switched by two Bosch automotive relays that are controlled by the stock wiring harness.  The relays draw very little current so heat and arcing in the switches isn't a problem.

The harness includes a male H4 plug so there's no cutting into the stock harness, if you want to remove it, the bike is still stock.

The kit includes everything you need to install the harness except for some common tools.

Tool list:

• #2 philips screwdriver
• #3 philips screwdriver (for the battery terminals)
• wire cutters (to trim the cable ties)
• 6mm allen wrench (rear tank bolt and headlight aim)
• 10mm socket (front tank bolt and battery box bolts)

    Click for a very large picture.

What are the options?

There aren't a lot of options.

The standard ones are:

• Korean made, no-name 100/80 watt bulb.  This is not a "tinted" bulb.  read this note
• Extra parts for dual light setup.  This doesn't include the lenses or reflectors or mounting hardware or anything.  This is if you already have a dual light setup and need the harness to plug into it.
• Removable Diode to keep the low beam on when the high beam is on.  This is quite useful if you've got a dual light setup that has one low and one high beam, or if you just want more light.  The stock reflector has a plastic lens, and I've heard that over time the plastic can discolor from the heat, although I don't think I've heard any first hand reports of this, just that it's possible.  If you've got a glass lens (like from an SV650) it shuoldn't be a problem.
  I wouldn't recomend using both the diode and a high wattage bulb, that is a lot of power for a single bulb and a lot of heat.  Also, 180 watts is s significant portion of the total available output from the Hawk's alternator.

I've got an aftermarket fairing with dual headlights, what about that?

• How far apart are the bulbs?  (center to center)
• What kind of bulbs does it use?  H4?  H7?  Something else? 
• How would you like them wired?  Some setups use one for high beam, one for low beam, others use one for both, one for high only, others use both for high, both for low.
• probably some other question that I can't think of right now.

What about my CBRGSXRYZF 600 or my '72 Bultaco?

If you want to know if it could help, measure the voltage across the headlight when it's on, if there's a significant drop compared to the voltage at the battery, then the wiring is wimpy and could be helped.

If you can find a place for the relays to mount gracefully, and a way to get a bunch of wires from there to the battery and headlight, then there's potential.

How much does it Cost?

Unfortunately Paypal charges me 5-6% or so.  My margin on these is small so I've got to make it up.  Sorry about that.  However, you can pay with a credit card.

Shipping is $8 flat rate via FedEx Ground for the lower 48 states.  For AK, HI, Canada, or other countries, send me mail and I'll find out what it costs.  I'll entertain faster/other shipping options, and even rush "Build me a custom one now!" orders, but since I don't necessarily have a finished harness waiting around to be shipped, anything faster than ground might be a waste of money. 

For weird setups (project bikes, funny fairings, stuff like that) Send me mail and we'll talk about it.

How do I order one?

Is installation hard?

No knowledge of electricity or mechanics or physics is required. 

If you can read and you aren't color blind, you can do this.

Paper instructions are included, and an HTML version is available here: www.mahonkin.com/~milktree/headlight-relay-harness/instructions.

Typically I hear that it takes less than 1/2 hour.

Do I have to worry about power consumption?

Not really.

Technically, if the bulb is running brighter, more power is going through it, which means the alternator has to generate more power to keep up with the draw. 

The power draw is increased if you use a dual light setup, or high-wattage bulbs.

However, it's not really a concern unless you've got two 100/80 watt bulbs running both high and low beams, and you've got an electric vest, and electric socks, and gloves, and pants, and ......

I'm exaggerating, but really you don't have to worry about it.  The alternator is rated at 240 watts at 5,000 RPM, and the bike (without headlight, but with gauge and running lights) draws about 60 Watts.  If you include 110 watts of dual 60/55 watt low beam, it's still only 170, leaving a resonable margin.