If they are wired the same as the Canadian HJ60, which uses 24 volt for everything except the headlights, then this may be helpful:
Are they the truck-llite bulbs?
Rudi, interesting stock/oem setup. Seems like a daft idea though (from a battery balancing idea) versus having 24V lights to start with. And if one of those 12V headlights go out while out in the sticks, then you have a balancing issue or driving only during the day...
The older 24V patrols always had 24V headlights - never realised that toyota had a major brain fart in their implementation.