The smart way to connect driving lights to a motorcycle

[Sidecar Bob]

Several years ago, Peter Hoogeveen wrote an article for Cycle Canada on preparing a bike for the Iron Butt.
In the Iron Butt, you spend a lot of time at high speeds on deserted roads at night, and good lighting is absolutely imperative.
Most bike charging systems (partly due to weight considerations) don't have a lot of excess capacity. Certainly not enough to allow regular use of a pair of 55W halogen driving lights in addition to the original 55W headlight, but most have enough capacity for one extra driving light.

What Peter does is:
- Connect the right hand driving light to the high beam and aim it directly ahead and level so that it increases the high beam's effectiveness.
- Connect the left hand driving light to the low beam and aim it so that it's light hits the shoulder of the road about twice as far away as the low beam hits the road. This allows you to dim your lights for oncoming traffic while still having some of the benefits of the driving light.

The driving lights can be controlled with a double pole single throw (DPST) switch.

I have tried this and it works.

Note: for maximum effectiveness, the driving lights should be mounted as high as possible. The lower they are, the less light will actually project down the road and the more light will merely illuminate the road close to you.
I had the lights on my trike mounted on the front of the fairing, just below the windshield. It made it look kind of like a big frog, but they worked much better than on previous setups where I had lights mounted below the fairing.

[Sidecar Bob]

After I posted the above I found some nice low profile driving lights with 35W H3s and plastic housings and mounted them on a light bar made from a piece of 1/2" square aluminum painted black to match the lights and attached to the lower triple clamp.

The plastic housings mean that the bulbs are completely isolated from ground so that I was able to wire them to a DPDT switch so that when the switch was down they were in series across the low beam and when the switch was up they were connected as described above. The two 35W bulbs in series only consumed 17.5W. Since my front turn signals didn't have running lights this meant that the driving lights only used a bit more than the original equipment most of the time and less than 30W more on the highway at night. The alternator can easily handle that.

I was very happy with this setup when the 'Wing was a solo but when I added the sidecar I changed to a bixenon HID on the bike and a low beam only HID on the sidecar, which lights up the road better than most car headlights.

I decided that I liked the look of the low profile driving lights so I replaced the halogen bulbs with 1W LED H3 replacements and connected them to the left marker light wire so that they turn off when the turn signal is flashing.

[Sidecar Bob]

Note that the advice in post #1 of this thread is still valid if you are adding 55W (or even 35W) halogen driving lights.

But a couple of decades on things have changed and halogen vehicle lights are no longer the best option. LED driving lights draw a lot less current for the same amount of light so you may be able to connect them in the conventional manner with a simple SPST switch to turn both on at the same time. It is still a good idea to aim the one on the side closest to the centre of the road (left in North America, right in the UK, Australia &c) so that it's light hits the shoulder of the road about twice as far away as the low beam hits the road to reduce the chances of dazzling oncoming drivers.

One caution about LED lighting (both vehicle and home): Don't go by the largest wattage number on the package when deciding how much a circuit can handle.
The true measure of how much light any device (light bulb, headlight &c) produces is the lumen rating and the actual power consumption rating (watts) only tells you how much power they use to do that. Unfortunately incandescent lights have traditionally only been labelled with the power consumption so people had nearly a century to get used to thinking of how bright a light is in terms of the watts consumed and a lot of people are dumb & lazy and refuse to make themselves understand that a light that uses less watts can be brighter. So knowing that many (most?) manufacturers & sellers put the "equivalent" rating in large print and you need to search the fine print for the actual power rating.
As an example, a few years ago I ran into a situation where there there were several recessed lighting fixtures in a basement ceiling that were rated for "60W maximum" but with 60W incandescents there was barely enough light to read a printed page right under the light. After convincing the homeowner that the rating on the fixtures was based on how hot incandescent bulbs got and not how bright they were we installed 13W (100W equivalent) LED bulbs and now you can actually see what you are doing there.

Marketing people being what they are, they almost always want to tell you the largest number possible and hide any smaller numbers so the actual power consumption ratings of many aftermarket LED vehicle lights are not given anywhere, making it hard to compare brightness based on specifications (is that "25W" LED light really, really bright or is it only equivalent to a 25W incandescent?)

Fortunately, what you really need to know when deciding how to wire them safely is really just the current they draw and if you have a multimeter and know how to use it that is pretty simple to measure (if you don't know how to measure current there are many tutorials online).

FWIW, I have changed the LED driving/marker lights on Mr.H twice since the picture above (see my How a Motorcycle evolves thread - link in my signature) but they are still mostly marker lights because with two HID headlights I don't feel a need to install bright driving lights.