1993 Nissan 240sx Speedometer ISSUE...Need help asap

[maz]

I just bought this new (to me) 1993 Nissan 240sx 5spd etc all the goodies

it has an issue with speedometer- it will work on and off...-i hit bump it will sometimes work then others not...-it seems very jumpy...not steady at all it will read lets say 60 then jump to 100...

What could this be? I was told it can be the cable? if so were is it and how do i get to it to fix it..

Thanks for reading and if there is any info it would be nice...

(pics help alot)