Speedo Sensor Needed

[Timbollew]

I've still not had a chance to take a look at it, but there's been a development. This morning on the way to work same thing speedo jumping around crazy. I switched of my headlight and the speedo returned to normal, I then stopped at some lights and thought lets try some other stuff, If I have the brake light on all ok but brake light on and indicator on it bounces up and down in sync with the flash.
Surely this means it's not the drive dog? Gonna have to have some investigative work this weekend, but I hate electronics  :'(