my 1965 mustang won't turn over even after i replaced the battery.

Check the positive & negative wires. Make sure the negative is tighted i believe to the block or fram & the postive is conected to the alternator. Also check your solenoid. & if none of thats the problem, then check the ignition.

is there power to and out of the starter solenoid when key is turned to start???

I had that same problem, it happened to be the Neg. cable, it wasn't connected to the motor. Before you go out and buy a new battery, jump the car, and then loosen the Nev clamp from the battery, if the car stays running, the the Alt. is charging, if the motor dies, then the Alt. isn't putting out enough volts. normal volts should be 13-14 volts. then i would loosen the connections to the volt regulator pos.& neg.and clean them real good, and tighten them back up....hope this helps