fuel guage has to be a matched ohmage as that of your sender in tank, my original one in dash was poo, i went autometer i think.another prob i had was the fuel pipe from sender in tank was a source of an earth from the electrical sender in tank,ie had to have a decent earth path, this had given me probs,most problems <as somone mentioned> are crusty earth points to car body and poor connections, these get hot and melt etc.some of my wiring cables had fried halfway through and looked ok each end, even gave continuity but would not like any real current going down there,also scotchblocks,twisted joints, my bulkhead connections fried but them its had 40 years of crap british weather.