If you have a "test light" you can solve this quickly.
First you have to determine if you want a power source that is "constant hot" (like what radios use to remember station presets) or a "key on" power source, which is more commonly used to allow the radio to play only when a key is in the ignition.....
With a test light, you will be able to determine what OTHER fuses in the fuseblock are "constant hot" and which are "key on" power sources....from there, the decision about which one to use should become clear. /forums/images/graemlins/cool.gif