Headlight relay harness for Honda NT650 Hawk GT

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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?

It's is caused by two things. The first one is hard to fix, you can swap it out with a headlight bucket from a Honda 919, or Suzuki SV650, or GSF400, or some other bike, but that requires special parts, and won't look stock, and... well, you'd have to think about it.

The wiring is deficient for several reasons,

The brightness of a bulb is determined by how much power you can pump through it.  The amount of power is determined by the voltage across it. The voltage across the bulb is determined by the source voltage and the resistance of all the wires and switches between the source and the bulb.

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:

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:

picture of the kit    Click for a very large picture.

What are the options?

There aren't a lot of options.

The standard ones are:

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

For $9 extra (and some measurements) I'll make it work with your fairing.  I'll need some information about the fairing before I can build the harness first:

What about my CBRGSXRYZF 600 or my '72 Bultaco?

What's listed here is for the 88-91 Hawk GT only.  If you can give me lots of measurements, I'll entertain setups for other bikes, but you'll be expected to do a lot of the measurements and the research.  If we do something, you will take full responsibility for the fit, and any potential benifit.  I'll gladly help you, but I can't guarantee how well it will fit, or if it will help.

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?

Stock harness$50
no-name Korean made 80/100
watt bulb (ea)
dual light setup9
removable diode for low beam
use with high beam
shipping (flat rate)8
paypal charge3

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?

Send me mail and tell me what you want.  I accept paypal or money orders or even personal check if I have some idea of who you are or if you're willing to let it clear before I ship.

Is installation hard?

Nope, it's pretty easy.

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.