If you are unhappy with the headlight bulb that comes with your four-stroke Honda XR400 motorcycle, you can upgrade it yourself with a bright headlight. The XR400 comes with an H4 55 watt halogen headlight bulb. You can replace this bulb with a halogen headlight up to 135 watts. The higher wattage bulb has the same amperage as the 55 watt bulb. In other words, it won't melt the wiring harness and can be powered from the factory-installed battery.
Turn off your XR400 if it was on.
Use a screwdriver to remove the cover around the instrument panel by taking out the visible screws. Pull off the cover.
Put on your latex gloves. Press inward on the side tabs of the wiring harness. Pull the wiring harness off of the headlight bulb.
Disengage the retaining clip holding the headlight bulb in place. Pull out the headlight bulb.
Insert the aftermarket headlight bulb into the headlight assembly in the same way the previous headlight bulb was set. Replace the retaining clip to secure the new bulb. Plug back in the wiring harness. Replace the cover.