1982 300D Stereo Wiring Question

[dailydriver]

Hi guys

I am a newbie to the forum.

I recently purchased a 1982 300D TD and am slowly fixing some things on it. One irritant is the stereo that came with. It is a Sony CD player. Everything is fine except for the fact that it doesnt retain the memory presets on the radio when i completely switch off the ignition. i have been told that i should connect one of the power wires from the stereo to the always hot wire from the car.....but what does it mean ? here is what i have;

I have pulled the stero and am looking at the wiring.....there is a yellow and a red wire coming out from the back of the stereo and is coupled to the red (hot) wire from the car. According to the stereo's connection manual, the yellow and the red wires are indeed meant to connect with the positive (hot) wire in the car. i have checked with a tester that the red wire from the car is alive only when i turn the key in the ignition one click to the right.

The other wire coming from the back of the stereo is black and that one is connected to the brown (ground ?) wire of the car.

so can you guys pleas give me any suggestions about how and where to connect the yellow and red wires from my stereo so that i dont have to set the time and memory presets every time i switch off my car.

thanks