Test D: Brake Fluid Level Switch

Remove the reservoir cap. Check that the float moves up and down freely; if it doesn't, replace the reservoir cap assembly. See Fig 1.
Check for continuity between the terminals with the float up and down. There should be continuity with the float down and no continuity with the float up; replace the reservoir cap assembly.

Fig 1: Testing Brake Fluid Level Switch

Courtesy of AMERICAN HONDA MOTOR CO., INC.