2) Due to the difficulty of checking the contacts of the wiring harness terminals on the components of the electronic injection system, a new wiring harness must be tried. 3) Carry out a road test. If the trouble persists disconnect the excitation lead (yellow sleeve) from the alternator, insulate it, and repeat the road-test : If the trouble disappears : either the alternator or the regulator is defective. Check them and replace whichever is faulty. If the persists: the electronic control unit is defective and must be replaced.