Can Accessory And Constant Wires Be Together?

I removed the old aftermarket stereo which had dodgy wiring. I'm installing Pioneer DEH-P7400MP which I had lying around. Anyway, it has 2 wires for power - yellow for constant and red for accessory. My car doesn't have accessory wire. The red wire from car is thicker than the yellow in my new head unit, would this be problem or should I connect both power wires from stereo to the red wire from car? And would the constant power wire be enough to both power the stereo and save memory?

If you don't have an accessory wire in the radio harness, you have one elsewhere (ignition harness, cigarette lighter, etc.). What is the vehicle?My ex once told me I have a perfect face for radio.

It's a 1995 Fiat Punto. My biggest concern is whether it's ok going from thicker wire to thinner one and not use acc wire at all. I don't mind radio staying on when I turn the car off.

As long as the thicker wire is in the car, and not on the stereo, this shouldn't matter.My ex once told me I have a perfect face for radio.