Turn on the iPhone, iPod, or radio and make sure you have a strong, clear signal. Adjust the volume to medium-high. Insert the phone plug at the end of the audio cable into the headphone jack on the iPhone, iPod, or radio. (When you do this, you'll no longer hear the radio, since the signal is being fed to the headphone circuit instead of to the speaker.)
Be sure there is no tape in the tape player, and then press the play button. Adjust the volume control on the tape player to medium-high. Since there is no tape in the player, you should not hear any significant sound.
Bring the wire-wrapped bolt near the play head of the tape player (where the exposed portion of the magnetic tape in a cassette would be located if the cassette was in place) . You should hear the sound from the iPhone, iPod, or radio playing through the speaker of the tape player. Remember: if the player doesn’t have its own speaker, you’ll need to have the headphones on.