Weak headlights

First check the voltage at the headlight terminals. It is probably less than what's at the battery. Most vehicles use a too small wire that goes through the headlight switch down to the lights which results in a lower voltage at the lights due to the amp draw from the lights. The best option is to add a relay so the wires from the headlight switch go to the relay that you mount near the lights. Then run a larger gauge wire to that relay then to the light. That will give you a higher voltage and more amps at the light which will give more light.
If that isn't enough then you could change the lights to better ones and will still have higher voltage at the lights.
Do a search for this upgrade.