Join Date: Nov 2008
Location: Kitchener Ontario
Mentioned: 25 Post(s)
What Year is Your Bike
One thing I can say for sure, it won't be the heat.
You don't mention,
#1- is this low beam on only
#2- have you pulled the light bulb, I have seen a bad bulb, from vibration, the filament was partially shorted--although on low beam that isn't enough to blow the fuse
#3 -what size of fuse are you installing
#4- check your output voltage, by adjusting your idle to 2000 RPM with idle screw-low beam only, should be 14.9 VDC or less--common problem if you have a MK-1 or MK-2 without a hugger or mud flap, the brown wire from the key switch controls the regulator shunt/ over voltage function--corroded connection and blown fuses --another easy but crude test is rev your bike from 2000 RPM to 4000 with both low and high beam on, if the higher you go the brighter the bulbs get is a good indication your regulator isn't functioning correctly. The stater has sufficient power at 1500 RPM to drive the low beam, there should be no change in light output no matter what RPM you are running at above 1500 RPM
#5--others have suggested to check you wiring, the passing switch / high beam is part of a flexible harness that has been known to be damaged by the clutch cable if it isn't routed properly- you could try turning your steering left to right while idling and see if a fuse blows
personally it would be faster to trace the wiring and look for a frayed connection / bare spot.