The easiest way to improve the headlamp circuit and supply "all available" power to the bulb would be to use a relay setup.
This is true since it increases available voltage, but it also drastically reduces the life of the bulb. Mototcycle Consumer News tested an aftermarket relay setup and found that bulb life was reduced by 75%, as halogen lights are sensitive to voltage variations and like running at 12V. Running directly off the battery increases that to 13V or more. Put a VOM on your headlight connector, then on the battery, both while the bike is running above idle and you'll see the difference.
That said, the test did reflect a noticeable increase in light output, so there's a trade-off.
By my calculations at 100 watts you should be pulling 8.0 amps. My guess is the wire is either 16 or 18 awg in size. You are cutting it pretty close. What you need to be more concerned with is your connections and hope Harley made all their crimps good and tight.
The passing lamps are wired in series with the low-beam circuit, and you could then surmise that both the headlight wiring and switch are designed for 55 plus the wattage of the passing lamps, which on my old RK was 50W total (25W x 2). Since the high-beam wiring is the same gauge size we should be good for at least 105W total on both high-beam and low-beam. I have no passing lamps on my SG so I should have no worries running an 80/100W bulb, and so far I've had no problems.
OTOH if you add 80 + 50W (high-output low-beam plus passing lamps) you go over that 105W threshold, but the wiring may still be able to deal with it. OTOH if the guage size is marginal there may be a decrease in output as a result. I put some 35w halogen bulbs in the passing lamps of my '96 RK and with the 80w low-beams it caused the 15A beaker to trip frequently, so I connected a common automotive relay ($5 at Auto Zone) to the passing lamps only. I had no trouble with it for the next eight years when I traded-in the bike.
08-19-2010, 09:58 AM
