If you don't have a meter to test battery/alt output (you should) you can start with the poor mans test, a screw driver tip to the back of the alternator shaft bearing located in the center at the rear of the alt case, as the vehicle is running, you should have a strong enough magnetic charge to hold the screw driver tip to it, if there's no magnetism, then chances are no output on the alt, if there's output but the battery is not charging, then chances are the voltage regulator, a battery that's given up the ghost, or a wiring issues...get a meter, you need it to take the guess work/ghosts out of the picture