Wobbly speedometer

[gergo]

Hi guys, this morning I had a flat battery in my ute so I've swapped in a spare battery and now my speedometer needle just kind of wobbles around between 10km under and over what it should be reading and drops sharply when brakes are applied. Under acceleration it pretty much reads proper, but occasionally bounces around.
Anyone by chance have some advice on what could be going on?
Ute is a t5 manual, incase that'd be necessary for figuring out whats happening

 

[losh1971]

Start by checking the cables at the speed sensor. They can become brittle from exhaust heat.