INDICATING A FAULT WHEN AT IDLE

QThe indicators of my Lancia Y10 flash at double speed when the engine drops to idle with the headlamps on. Could this be caused by an earth fault in the front lights?

Rick Jones, Warminster

Nigel says:

AWorth a try – and clean the fuse for the flasher unit – but it’s most likely a weakness in the main electrical system. The headlamps cause a voltage drop, which reduces the current in the flasher unit and fools it into going into bulb-failure mode. Since it doesn’t happen at higher revs, we can conclude that the system is getting a good supply from the alternator, but the battery can’t supply the shortfall at idle, when the alternator generates less current. Look for a medium-duty cable which connects the battery and alternator. This may be the culprit – check it for damage. If you have a multimeter, compare voltages throughout the system with the voltage at the battery. Up to a 0.5V drop is acceptable. 1V or more is a problem.

Voltage throughout the whole system should be within 1V of the battery voltage.