to check gauge momentarily (few seconds)ground wire at sending unit and note full scale deflection. if so then sending unit is bad or needs cleaning. i just removed mine and cleaned wire wound resistor inside housing with fine sandpaper/steel wool and then checked resistance from one end to other noting no discontinuity - goes from about 10 to 82 ohms. seen many failures of repro units here on Forum and original looks well built. by way check that float isn't flooded and if you buy new sending unit take a look at AMK - they advertise one that has better construction but was priced a bit higher.