Just swapped my radio using a similar kit to the one linked above and found that the ignition feed doesn't work with my new radio. I've had to connect the switched (ignition) feed with the permanent feed. The switched feed appears to be 7V when the engine is turned off and 4.5V with it turned on. Why on earth they can't use a standard 12V fixed feed for the ignition switch I've no idea!
All I gotta do now is remember to turn the radio off when I get out of the car or the battery goes flat - either that or run a wire from the cigarette lighter to the switched feed on the radio thereby allowing the radio to turn off with the ignition.