Try disconnecting the lift pump plug, and bridging ta wire between the purple wire and a brown wire, this should make the fuel gauge shoot to max. If that doesnt work pull the clocks out and check round the back of the fuel gauge, it should be held to the clocks with small nuts, these also provide the electrical path to the pcb so if either of the nuts is loose or missing then it wont work right. You could try another fuel gauge, or just swap another set o clocks in!
the speedo probably just needs throwin in the bin and replacing, not really much you can do to fix em

theres no relay for the dash
