Vw_audi_guy

Got the car not long ago . Gas gauge didn't work . The (po) said the fuel pump had been changed recently and that the gauge stoppe working . Once I got it I started doing research and reading forms about the same issue. I tried pulling the fuses for the fuel pump and the – 15 and 28 I believe it was. That did not fix anything. So I pulled the backseat . There was two covers underneath I took both of them off. The one on the passenger side was apparently the fuel pump so I took the other one out, there was plenty of fuel in the tank. The arm with the float moved freely I checked for voltage and there was none. I believe that runs off of an ohm resistance. I then did more research and found out about the plate underneath the luggage compartment I took that off and removed that as well, which looked like another sending unit. The cavity that it's set in was bone dry as well as the float. Both sending units have the same connection on the outside a blue and black wire .so I'm guessing maybe it's a secondary sending unit I'm not sure. What I'm trying to figure out is how to test them whether it's in on reading or it's a voltage.