i didn't really want to do that because if the charging system fails, the lights would go off. that might sound like an advantage, but i don't want the lights going off for any reason when its running.
You could get all fancy with an ammeter kicking the relay on going into positive charge. Or You can be the intelligent controller with a Switch.... <<<)))
My Honda simply had a relay coil connected to the starter switch. The NC contact on the relay was in series with the headlight. That disconnects the headlight when you activate the starter, which is all you need. The short draw of headlight current between the time you turn on the ignition switch and activate the starter normally has negligible effect on the battery charge.