iPod stops, shows error

[waydre]

I finally got around to hooking up my iPod with the USA Spec iPod Interface PA11GM but I'm having a lot of difficulty.
You know how the radio and other things will continue to work for around 10 to 20 minutes after turning the ignition off. The RAP "Retained Accessory Power" feature.

If I'm playing the iPod while the ignition is on and I turn the ignition to off the radio stays on as normal but after a few seconds the iPod will pause, give me an error message and the radio will jump to FM band and the radio will play.

The iPod will not play again until I unplug the USA Spec PA11GM and plug it back in.
This happens everytime I turn off the ignition.

I'm thinking the iPod Interface is not wired to Retained Accessory Power therefore pausing the iPod with the ignition switch instead of the radio.
But I haven't heard of anyone else having this problem.

Does anyone know what is causing this?
Which wire on the radio wiring harness is for the Retained Accessory Power?