Check out this thread ...
http://ducatisportingclub.com/contro...d.php?tid=4116 Switching a Higher Bulb Wattage
The stock light switch is designed to switch 55 watts. In order to switch more than 55 watts you should use a relay that is sized for the higher wattage and then use the stock light switch to energize the relay. You also should use a thicker gauge wire between the battery, relay and bulb to handle the additional current draw. Also, even though the light assembly is glass the additional heat of (say) a 110 watt H1 bulb has the potential for melting any non-glass components nearby.
Electrical System Overload
Just the use of one 110 watt bulb exceeds the design capacity of the 916’s charging system. The reason that early 916’s only operated one headlight at a time is that the marginal charging system design can’t handle two 55 watt bulbs simultaneously. The problem stems from an electrical system design that includes a charging system of marginal capacity that results in constant high electrical demands on the components to maintain an adequate charging rate. The weakest link is the regulator. The problem is compounded by faulty stators, poor electrical connections, small-gauge wires, and inadequate cooling of the regulator itself.
[Edited on 11-30-2003 by Shazaam!]