Help with reading ADC 3.3 Analog Input of Pixhawk


I am trying to figure out how to read the analog input of pin 13 on the pixhawk (ADC 3.3). Currently, I have pin 14 setup to read the sonar voltage (even though a sonar is not attached) and it works perfectly. How can I read pin 13? I have tried setting it up as the Battery Monitor 2 and as the analog voltage input for RSSI but still can’t get any readings.

Didn’t realize this would be so difficult. Any help would be appreciated! Also, as a note I am using Copter 3.4.6 and would like to keep this version as other things I’m doing require this version.