If you bypass the switched power lead by using a direct connection to the battery, the radio will remain ON when the key is removed which is not good. There will always be that one time you turn the volume all the way down and forget to turn off the radio and then the car won't start after sitting for hours.
Adding a large capacitor in line with the switched power lead will probably do the trick, but it will cause the radio to play for several seconds after you remove the key until it completely discharges.
Either way, you will need to know which wire is the switched power lead for the radio.
Adding a large capacitor in line with the switched power lead will probably do the trick, but it will cause the radio to play for several seconds after you remove the key until it completely discharges.
Either way, you will need to know which wire is the switched power lead for the radio.