a) Loose alternator belt. b) The rotor and stator windings are short-circuited or damaged. c) The graphite brush spring is weak or the brush contact is weak. d) Loose terminals.
a) Tighten the belt or replace the worn belt with a new one. b) Restore or replace the rotor or stator with a new one. c) Restore or replace the graphite brush spring with a new one. d) Check and tighten.