Open the cassette player case and locate the metal square magnetic reader. On either side of the reader are a pair of wires. Snip the pair that has the red wire and strip the ends.
Attach the stripped wires to the positive connector on the female 1/4" jack. Wrap a small piece of electrical tape around the wire. This will prevent the wires from fraying and touching the ground connector.
Snip the other pair of wires connected to the square magnetic reader. Strip the ends to reveal the bare wire. Attach these to the ground connector on the female 1/4" jack. Wrap a small piece of electrical tape around the wires.
Plug the instrument cable into the phono jack or the headphone jack. Plug the other end of the instrument cable into the female 1/4" jack. Plug the cassette player into a power source.
Turn on your keyboard and turn the volume down. Turn the volume up on the cassette player and push the play button. Slowly turn the volume up on the keyboard while playing with the keys. Adjust the volume until you have reached the level you want.