A vehicle having an electrical system including an electric power generator arranged to selectively provide electric power to an electrical load of the vehicle and to selectively charge a battery of the vehicle. A fault detection system is provided for detecting an open circuit or high resistance fault in a ground circuit. The fault detection system includes a controller that controls a voltage output of the generator so as to either restrict or suspend charging or increase or start charging of the battery by the generator for a designated test period. A determining means determines a current discharge from or charging current into the battery during the test period, wherein if the determined current discharge or charging current is less than a given threshold, then an open circuit or high resistance fault is deemed to be detected in the ground circuit.