Any one know how?

I have a 1 farad cap that i was using, it was charged by the previous owner, this past week i uninstalled my system and reinstalled it with some diffrent components, hooked it up and the cap turns on but dosent have any numbers on the Digital display like before. I was playing the music for awhile and a led started blinking red and i quickly shut off the car.

I think the cap needs to be charged or something since there is no voltage numbers being displayed on the cap.

anyone know how to charge a cap, correctly?