this is a old fault from when i bought the car, can't find voltage regulator or tank earth

By 'earth' between sender and tank, I mean that the body of the sender unit should be making good electrical connection with the body of the tank where it fits. Similarly, the tank itself should be making good contact with the chassis - usually this is via the retaining straps or fixing bolts.

Also check the simplest part - the 'live' push-on (?) connector on the sender.

Thanks to Donnie for the info will do some sorting out. Ned

Good luck with it Ned.

Don't forget you are working with a combination of petrol and electrickery...

If we are talking MGB based here, then it is likely to require a ballast resistor in the line, which is usually screwed to the back of the speedo (or is it tacho)! The purpose of this unit is to damp out the fluctuations caused by the fuel moving around in the tank when moving and acting upon the sender unit.

As advised, check connections and earths and consult the MGB wiring diagram.