The resistance of the fuel tank sender will vary based on its position in the tank... . it will range based on the fuel... . I don't know the specific ohm readings but I'd connect an ohm meter and if its not grounded or open I'd assume it would function... ... ... ... if it passed any of these tests I'd pull it from the tank and do a bench test with the specifications and move the float... . If you read empty all the time expect to find a sunk float or one that has decayed from chemicals added to the tank.....
On the newer trucks, the alternator is controlled by an ECM... . it varies the voltage back to the battery based on the cold air senor on the motor... . colder air, more battery resistance to charge and a higher voltage... ... hotter air, warmer battery, less resistance to charge and lower charging voltage... ...