Suzuki Club UK

My fuel gauge is very erratic to say the least. I put £20 in the other day & it eventually showed about a quarter of a tank but is now not registering anything (only done 70 miles). The guy I got her off told me it never worked properly since he had owned it & he'd put a new sender unit in the tank & that didn't cure it. He seems to think it's the wire running from the sender to the gauge. Is this a common fault & if so, easy to rectify?

Sorted it it was a bad earth on the sender unit. Couldn't get the screws of that hold the sender in to tap an earth to (I think they're made of chocolate) & tried for ages to solder a wire to the top of the unit but couldn't get the it to stick
In the end, drilled a pilot hole into a badly butchered screw, popped a small self tapper into it & attached a wire connected to the bodywork
Not pretty but works!