Spent a few hours attempting after market radio install on my 87 240 DL and I need some help/suggestions for wiring, I figured the speaker arrangement out using a nine volt battery.

My next issue is as follows I will attempt to be brief. I have determined the Volvo wire colors,
green ( does nothing I can determine yet)
Red/black (power)
Black (ground)
My radio is a kenwood it has power (red), ground (black), and yellow (battery)
The yellow wire has to have constant power and this is the problem I need help with. The old aftermarket radio I removed was connected to the green wire (volvo) but this I soon learned was why the old radio did not maintain radio memory, Thought of tagging it in with cig lighter but this does not have constant power and ignition has to be on for it to work. I could go directly to the battery but would need a inline fuse and don't want that much work if there is an easier way.

I await the rush of all valuable input!