As I recall, the two common values were around 90 ohms and 10 ohms. The resistor can't read too low. If you're reading 0 ohms from the dash, the wire going to the sending unit is shorted to ground. If it's reading very high, look for corrosion in a connector terminal. If it's reading open, the wire is broken or the wiper on the sending unit isn't making good contact. Measure right at the sending unit to see which one is open.