[QUOTE="Iain Chalmers"] See my other post - wikipedia and the back-of-the-envelop suggests 1 decilitre per hour is pretty close to what your 120W headlights require... Can I get you to do another experiment? I'm wondering if 800rpm is too slow for the alternator to be developing all the required output, and what you're seeing is the headlights drawing the battery charge down rather then being powered by the engine. I'd be interested to know if you see any fuel flow difference in the diagnostics if you hold the engine at a slightly higher speed when you switch the lights on and off - maybe up at 2500 or 3000 rpm? curious-big[/QUOTE] The fuel computer on the Holden 5.7 litre is not very accurate so it is unlikely to provide the information required. Boxer