You can put both on positive
You can put both the red and yellow wire to the positive. The yellow wire is designed to be always hot so that the redio keeps it pre set stations and clock. The red wire is designed to be hooked to a switched power source. It is fine to hook both to a switched power source such as an accessory switch in your power panel. If you hook both to the same accessory switch, when you turn off that switch, it will turn off the radio and lose the clock and presets every time you turn it off. If you want to keep the presets and clock, then connect the yellow directly to the battery and the red to the switch. If you do this, your radio will draw voltage even when the radio is not on, and will eventually run the battery down if you don't keep the batteries up.