Is the plastic cover scratchy and/or turning yellow? Could be they need to be buffed out. (Maguire's makes a kit that you use with a drill and it works great.)
Other than that.. it could be an electrical feed problem or possibly out of adjustment.
Your headlights may not dim because you don't have dimmer lights. Dimmer lights can blow and leave you with just the high beams.
I would suspect the dimmer switch or "combination switch".
The headlamp switch controls the power to the dimmer switch and then on to the headlights.The headlamp switch controls the power to the dimmer switch and then on to the headlights.
Regular Dimmer will work.
Dimmer switch is possibly defective
The dimmer switch is defective.
turn the dimmer up.
They as designed to "dim" when headlights are on to reduce "glare" try adjusting dash dimmer switch
Yes it could.
Dimmer switch controls the selection of either Hi-Beam or Low-Beam headlights
This is usually an indication that the dimmer switch is in need of replacement.
Bulbs? Fuses? Relay? Dimmer switch? Headlight switch?