Dead Fuel Gauge

[nut161]

this is my first post so hopefully I have managed to get it in the right section.

I recently bought an 05 ba mk 2 turbo ute and the story goes form the previous owner that a workshop installed a bigger intank fuel pump and ever since then the gauge was funny. it used to show empty when full and full when empty etc until it just completely stopped working.

now only being new to these cars is this jsut likely to be a wiring fault? or is it possible that the workshop broke something on the fuel pump/sender assembly?

thanks in advance for any help.