If you have a service manual it will tell you the resistance and how to ck it. I had to do this on my 2001 heritage. You have to remove float system from tank to do this. Use a good digital meter and move the float up and down checking the readings as you go. Good luck.
Info taken from 2002 Electical Diagnostic Manual for Touring Models.
Full fuel tank resistance 7-14 ohms on FLHT and FLTR models.
Full fuel tank resistance 27-40 ohms on FLHR
Empty fuel tank resistance 74-95 ohms on FLHT and FLTR models.
Empty fuel tank resistance 240-260 ohms on FLHR models.