best way ??

hi i have a savana gmc 2000 and i need to know which wire as power to connect a cd chnager without taken a part the dash board i saw the
antenna from the radio on the passenger side and i can splice and connect the input for the cd changer but for the power i am thing to connect the cdchanger power to the trailer power in the back or the driver side .. i can see lot wire from the alarm and more ????
any idea which is which standard wires ??? the red wire is direct from the battery and yellow from starter ???? some help please .... i don't have the manual of this cd changer toshiba tx-972 and i know is old 1992 :)) but in good condiction .
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