Speedo/indicator going crazy with revs?

[Greenzy03]

I’ve got a 2005 70cc Derbi Nude and I’m fixing it up. However, the indicators and Speedo go crazy when it revs or is jolted. The speedo will jump around from 5mph to 35mph if I Rev the bike at stand still and the indicators just go absolutely crazy. What could be causing this? I’m thinking a loose connection to low battery?

[Mississippi Bullfrog]

Put a multimeter on it to check the voltage as the revs rise. I bet they are going too high, in which case the regulator has failed.