Red Yellow and Black Wires?

I am trying to "reinstall" a Sony stereo into my Fed Ex delivery truck. The previous owner disconnected some of it and did a piss poor job of installing it in the first place. I need to know what the red, yellow, and black wires are for. I am assuming the black is ground, red is switched power and yellow is constant. Please help me out. The model of stereo is a Sony Xplode CDX-4000X if it matters. Thanks

You should check them with a digital mulitimeter to ensure what each wire is for before you hook anything up to them.2 Memphis HPO 12s

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switch, please read the post accurately before answering. He was asking about the DECK wires, not the car's wires... Yes, the black is ground, the yelow is "batt" and the red is "ign" or "acc".It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."