Designing a car steering wheel interface, need to distinguish between two resistor ladders on the same ADC
You would be better to have the default point referenced to mid-rail...

Something like this.







simulate this circuit &ndash; Schematic created using CircuitLab

That way the switches will adjust the voltages either higher or lower than the mid-point. R3, R4, and R5 provide a little isolation and should be &lt;&lt; than R1 and R2. Chose values for R1 and R2 that are in the same range as the resistors in the steering wheel times about 3. That should get you approximately the following voltages.



Also add a capacitor to provide you with a little noise reduction and to get rid of some of the switch debounce.

You may also want to consider adding some ESD protection.

In case you are not aware, the software needs to handle this kind of button scanning carefully. Since the voltage will slew through other voltages on it's way to the switch pressed value a certain amount of averaging and time comparison is required.



If the running average is deep enough the decoupling capacitor may not be omitted.