i have the same prob sometimes. with mine thou the speedo lights up with side lights and when i click over to headlights the speedo goes off. then i nudge it back a bit and then back to headlights and it comes on again. (this only happens when change to headlighst quikly with mine)
i'm guessing with mine it is corosion on the copper plate in the light switch.
this is my experience not sure if it is the same as yours.
check if lights up when side lights on. were you cleaning around light switch? may be a problem there instead?
edit: just read post before mine

_________________
Sunday Morning Mini Sprint
http://www.youtube.com/watch?v=UtGuzqBQ32Q my "rendezvous"