Black goes to ground.
Red goes to the power feeding the current AM radio
Yellow goes to battery on all the time (not switched) make sure it has a fuse.
Blue (amp signal) won't get used.
Speaker outputs...run to which ever speakers you add (package tray, or?
) If you are only going to keep the dash speaker, you might consider running a small pair of 3.5" speakers under there and run your speaker wires up to there.
That should get you going at least, pretty simple really