" I am using this diagram:
http://www.motoscrubs.com/Ducati_Electr ... iagram.jpg "
____ That colorized-version (scanned from an owner's manual) is adequate enough, but it's depiction of the (headlamp located) terminal-board ought to be enlarged so that all it's various wire-connections can be more clearly realized. _ I'm thinking about tackling that task. - (UPDATE - I've now done so, [as seen in the bottom-pic] !)
____ Since you've already removed some of the main components from within your headlamp anyhow, that would now make it more worthwhile to go-ahead & do some added wiring-modification.
These particular wiring-mods wouldn't be as important if the system has been converted-over to 12-volts but, the modification-logic (of reducing circuit-heating current-flow) would of course still apply.
__ First... the blue-wire to the ignition-switch ought to be changed (from 16-ga) to 14-gauge, OR better-yet, reroute the main red-wire (from the battery) DIRECTLY to the key-switch's normal/(blue-terminal)-input, (while leaving the stock blue-wire as normally electrically-connected, so as to continue feeding the parking-light as stock).
Next, (and at-least as important)... have the orange-wire, (which feeds the main-lights through fuse-19 / [# '9' in the expanded-views] ), rather get it's power-source (more directly), from the key-switch's normally unused 3rd.terminal, (instead of only [indirectly] from the terminal-board). _ That way, the key-switch's white-terminal & it's white-wire (to the terminal-board), don't have to conduct/carry ALL the power-juice/current-flow for the entire load-system, and besides that, the main-lights then won't have to draw their (large!)- share of current-flow through the terminal-board's jumper-connections (from the white-wire to the horn & brake-light fuse -[#8]) !!
So simply-put, this key-switch/wire-mod requires merely adding a 16-gauge orange-wire directly-from the key-switch to the main-light fuse, (leaving the stock orange-wire from the other side of the fuse still going directly-to the light-switch as stock).
This added wire-circuit will then allow splitting-up of all the current-flow* (through TWO output terminal-connections of the k.switch), that's drawn by the main-lights plus all the rest of the load-system, (*which is normally only handled by just the white-wire connection alone).
__ Ya may wonder why I'd bother to suggest this seemingly redundant wire-connection... Well I first came-up with this fix after installing 45-watt* sealed-beams on some w-c DUKEs, because I then later found that the stock key-switch's blue-to-white internal terminal-connection would get burned-up (and thus begin conducting very poorly [if at all] !). _ The quick-fix was to simply move the white-wire over-to the (normally) unused terminal on the key-switch, but while doing that simple reconnection-move seemed to solve the issue at first, it couldn't be trusted for long (especially with a greater than stock lighting-load). _ So whenever I had to install a new (stock-type)- ignition-switch, I'd then also make this particular wiring-modification. - (As seen in my [altered]- scheme-drawing, showing the added/suggested orange-wire.)
(* Keep in mind that while the "45-watts" may seem to be low-power, it's actually equivalent to a 12v.90w light-bulb in [circuit heating] current-draw !)
__ Also, the stock/(junky!) main/head-light's fuse-holder -(#19 / [9]) really ought to be replaced with a good/modern fuse-setup !
Mod.Cheers,
-Bob