Measuring external voltage on Arduino
Based on this article it would seem that what you are dealing with is "3 pedals that have varying resistance whether it is the brake pedal, accelerator, or clutch." So you really ought not to be taking a voltage measurement to determine your interface characteristics in the first place. What you should be able to do, rather, is disconnect power or USB or whatever from your controller and see which pair of pins exhibits a variable resistance when depressed, and record the range of resistances that you measure practically. Then set up an appropriate voltage divider circuit per pedal such that you can read the midpoint voltage with the Arduino analog input in the conventional way. These sensors do not "output a voltage" they "vary a resistance" so you need to wire them up withe external circuitry accordingly in order to translate that varying resistance into a voltage response that you can measure.