My battery and brake light come on intermittently on some drives and stays on during others. I checked the voltage output at +terminal on battery with car on 14.66V with fan load 13.6V. Engine off, 12.4V on batt. That was the first day and its been 3 days since now the light stays on. What could this be if NOT a failing alternator?

 

You can go to a local Batteries Plus or Auto store to get them to check the alternator.