Low brake fluid light stays on after replacing a brake line

Hello,

On the side of the master cylinder there is a brake fluid level sensor. When the fluid is low that sensor sends a low fluid message.
If the fluid is at the correct level and you are getting that warning light, it could be due to a faulty sensor.
You also want to make sure that the connector is secured to the sensor and does not have any corrosion.

I have attached diagrams for your reference.

Please let me know if you have any questions.
Thank you.