Electrical problems, please advise

Having some issues with the electrics on my Derbi 172. It will run fine starting with the kick start, but all the lights are knackered now. At first it was just the indicators that weren't working, but now none of the lights are and the speedo has started going a bit mental. The needle on it just keeps flying all the way round then bouncing around all over the place. It's not very helpful when it says I'm doing 80mph when not moving, and 0mph when travelling at speed

I have replaced the fuse which hasen't had any effect. Can someone please help me with what I should look for next. I'm thinking it is maybe a dodgy wire or connection not on right, but would be great if someone could advise me before I start checking all the wiring over. Electrics are a dark art to me, I'm lost.

Sent from my X10i using Tapatalk