[Edit - beaten to it - dawdled too long finding pics [:I]]
I'm not sure what variations may exist in various models, but on mine, a 1978 Speke built FHC for Australian delivery the red wire from the radio connects to a White/Pink cable that is switched by the ignition key. This wire connection emeges from the main harness with the Black/White speaker connection end points. (See pic below)
I did not connect the yellow continuous feed on my car as there is not a connection point for it and I don't mind tuning the radio it each time I use it. If you do want to connect this you will need to either run your own cable to the battery terminal (not recommended) or splice into one of the brown cables that carry live feed.
There are a few locations you could do this. The shortest distance to cable to would be to the butt join in the harness on top of the right hand side of the fuse box. (See pic below)