Yellow from the car is to be combined with red from the radio and vice versa. And it's best to take the instructions from the radio and read where the "fixed" plus and where the plus should be "after the ignition", and then determine on which wires the original installation is what (preferably with a "test tube" with a bulb).
http://download.sony-europe.com/pub/manuals/swt/Z012/Z012648111.pdf Two solutions will meet on car radios:
- In better aftermarket radios and most factory ones, the main power supply is constant, and the power supply "after the ignition" is only for information, to control the so-called "ignition logic" on the radio (there is practically no current in this circuit). Such radios can be turned on with the button, without the key in the ignition (but they usually have a timer and turn themselves off after a dozen or so or several dozen minutes), but of course they turn on themselves when the ignition is turned on (or rather they return to the state they were in when the ignition was turned off) .
- In cheaper radios, the main power supply is "after the ignition", and the constant power supply only serves to maintain the settings memory. These radios cannot be turned on when the ignition (or ACC circuit) is turned off.
Hence, by putting a cheap radio in the place of the factory, it is usually necessary to swap the power cables "cross-wise" (although this may cause a problem with the load capacity and protection on these circuits in the factory installation).
