29-05-14, 09:32 PM
The link below might be useful to you. Half way down the first page is a wiring diagram I did some time ago. It's for fitting the Foxeye headlamp with two dips and two main beams to a boxeye, but that sounds just the same as what you are trying to do. i.e two H4 bulbs. The Foxeye wiring diagram does it in a different way and uses different relays for the same result, but would mean more complicated changes to the main wiring harness on a boxeye model.
http://foc-u.co.uk/index.php/topic,5252.0.html
The thread that Fazerider gave is useful in that it shows how to get the feed for the dip relay, but it doesn't put the left dip out when you go to main beam. That's because on the standard boxeye left dip is on all the time and that mod is just brinking the right dip into play.
Hope that helps but just ask if the wiring diagram doesn't make it clear.