Oil level sensor- is on the bottom of the tank, you will see the wire going to it. I would take the wire off and clean it real good and put back on before I would be in a hurry to change the sensor. make sure all oil is out before removing but I would check brake switch first.
Brake sensor-Squease your brake all the way, you will see a de-tent type button which pushes in. That is the switch for the brake light and will be the one that activates the light on the dash also. Take and push and pull on it and see if the dash light goes on and off. On an 01 I had this switch would freeze up until my handwarmers got good and warm and then would work fine.