wvmarle:
Agreed. The existing internals are useless - you have no idea what it's doing, and it's for a very different purpose anyway.I guess you're going to need a second Arduino to do the actual controls: one in the phone that reads the buttons and controls the LCD, the second one is sitting somewhere on the other end of the curled wire and which does the actual reading of sensors and switching of the lights and whatnot. They can communicate over Serial, with your phone Arduino sending commands to the controls Arduino, and receiving sensor data back.
Do make sure you have a good power supply for them, as car electrical systems are notoriously noisy and prone to voltage spikes.
Thank you for the input! I'm new to this whole process so the help/advice is much appreciated.
I was planning to have the arduino in the phone give out a voltage when a button was pressed which would then switch a mechanical relay. Do you think having a second arduino would be better than this?
Also any recommendations in the power supply area??