steering wheel control

The jack on the back of the radio has 3 connections.  They are as follows, power, ground, and the return or sense wire.  The unit is controlled by voltage.  The power wire powers a string of resistors that are wired in series, the other end of the resistor network is grounded.  At each resistor junction, there will be a definite voltage.  When you press the switch at the appropriate junction, it will send the specific voltage back to the microprocessor, then the processor will perform the function that goes with that voltage.  I have no idea of the value of the resistors or how many you need for the chain.  Even if you are not going to use all of the functions that the unit is capable of, you will still need to put the resistor in the circuit.  I have no idea how many functions the Alpine units are capable of, nor do I know the resistor values for the Alpine.   The following diagram will hopefully help you a bit.  You may want to get in touch with someone at pac-audio.com and see if they can steer you in the right direction with the resistor values and how many resistors you need.  If you find anything out from them, please let me know what you find out.  I have an Infrared repeater on my Alpine radio that is mounted under the seat of my scooter.  I was planning to make a remote just as you are, but never took the time to get resistor values and such.  Maybe you are a bit younger and have a bit more stamina, and can complete the job.