Speedo Issue/Neutral light issue
 

hey guys
For a little while now ive been having a issue with my SH were i'll shift into 3rd or 4th gear and as soon as i start too accelerate the speedo goes start to zero. I've heard that it could be electrical but any ideas on what it could possible be? Also I have a issue were if i'm idling at a light and i go into neutral my neutral light doesnt come on, it also kills the bike, could my neutral safety switch be going? (I think thats what it is called)
Cheers
P.S.
has anybody done a full rebuild on one of these before? Is it worth doing or no?