My anti lock breaks light is on and my break pedal goes completely to the floor before stopping. My master cylinder is full
My car has 205000 miles.
My car has an automatic transmission.
Since the master cylinder is full and the brake pedal is going to the floor, there is a good chance the master cylinder has failed or there is a leak somewhere along the braking system. This leak may be found at the master cylinder itself, on a rusted line or one of the brake calipers may be leaking brake fluid. Consider hiring an experienced technician like one from YourMechanic who can come out to the vehicle for a closer inspection of the warning light and the circumstances causing it to offer a more personal diagnosis and estimate the proper repairs.