There are 2 power wires and 1 ground wire that needs to be connected for your Fusion Marine stereo to operate correctly.
Both the Red and Yellow wires need to be connected to 12V and the black wire to ground/battery negative.
The yellow power wire is the high current supply wire. This needs to be connected to your battery using a cable suitable for carrying at least 15 amps.
The Red power wire is a switched input. When 12V is connected to this wire the Marine stereo can operate. When disconnected the stereo will shut down and remain off.
The Red wire may also be connected together with the yellow wire if you are supplying power through a switch panel capable of 15A or if a battery isolator is used to disconnect the battery when not in use.
The yellow +12v wire in some Stereo's provides power to the memory of the unit for presets etc this only applies to Fusions MS-CD80 as Fusions 600 and 200 series Stereo's are designed to save all settings when power is removed.