See inside the bulb there are 2 little coiled wires. the one at the top is low beam, it has a reflector/ shield to stop the light from being above the light centre line. the lower coil is high beam and light can go every where in the parabolic reflector giving a flood light
They are H4 bulbs. I had my low beam burn out at one point too. I rarely ride at night so I didn't worry about it till one day I was stuck working late and rode home in the dark. Ofcourse on my way home the high beam filament burned out on my way home then. LOL I replaced it with these LED bulbs. They work fine, they are brighter than the super fancy xenon bulb I put in but you have to mess with the orientation of the bulb to make it shine in the right area. Not that big of deal but something to not. It is a 2 pack for that price. I gave the 2nd one away to a group member. If you go with an LED be mindful of any fans or heat sync off the back. Most won't fit and allow you to put the water right seal on. This one is tricky to fit it all in the housing and the water/dust seal but it will fit.
What about changing the TPS? I mapped it 2mo ago and recently only 2x the idle went low, and it actually konked out on me the first time...i was going slow in 2nd in my hood... i pulled over and cranked it up no problem the rest of the day
Tps needs to be taken in if we are talking about the 821/939. The headlight, 2 bolts under the beak, pivot out and push the whole beak up. The pins will pop out of the rubber grommets and the whole assembly will be in your hands. Then you just unscrew the back cap and reave the bulb. Very simple