Dito with NickH

A question I always wanted to ask about the Ducati 748 headlights... is only one side supposed to be lit when you have your lights on?

Yes - the units are "projector" beams, which means that they are only focussed for one particular spot on the road. You can tell this because if you look inside the lens looks like a really big magnifying glass!

This is why there are two headlights - one for dipped beam and one for full beam, ie. because of the lenses, you cannot have mixed full and dipped in the same unit.

The running lights (the little peanut bulbs, aka sidelights) are in both headlights, tucked in the corner, and these should be one all the time when your headlights are switched on.

But what about the 'Aussie' unit??

It shouldn't be any different to the UK model, as the Aussies also drive on the left-hand side of the road.

Unless their laws are different with respect to having both headlamps lit (which I very much doubt) then there doesn't seem any reason to be a difference.

The only other thing may be that the beam arcs are slightly different (higher?) but this would probably make them illegal in the UK anyway.

Maybe it's worth trying to cross-check part numbers?

There are two issues of concern here:

Light Pattern

The low beam is a projector head lamp that functions like a slide projector, using a plano-convex lens to distribute the light, rather than a parabolic aluminized reflector used in the high beam. They are used to give a sharper cutoff and they can be field-switched between left-dip and right-dip for use in Europe. They are more efficient than conventional reflector designs, because they are able to use more (and waste less) of the light than reflector-type lamps. However, because of the sharp cut-off low beam pattern (even at a higher light output) they are not suitable as a high beam light.



Electrical System Overload

The reason that early 916’s only operated one headlight at a time is that they had a marginal 350 watt charging system design that couldn't handle two 55 watt bulbs simultaneously without needing a constant high 30 amp charging rate. Newer 500 watt systems have the capacity but the weakest link is still the regulator. The problem is compounded by weak electrical connections, small-gauge wires, and inadequate cooling of the regulator itself.