How to know if a wheel cylinder is bad?

[twilightcall]

I appreciate everyones help. It is the light on the left of the steering wheel. It is the same light that is on when the parking brake is engaged. The pedal was going to the floor but still had slight resistance. I changed the master cylinder and bleed the brakes. The pedal came up but only around 1/2 way or slightly more. It stops ok. It just has a good amount of free play at the top (or pedal travel) before the car starts braking. I didn't notice the cylinders leaking at all. I inspected all of the brake lines and found no leaks. The only other item that I can think of would be the Brake Valve (proportioning valve). I am not sure if these go bad often plus they seem to be very difficult to find. It just seems that the pedal should be higher.