If it is similar to the Kenwood 790, one form of the control head (with eight character read-out) requires a power jumper among the pins to increase audio output to an external speaker, whereas the more familiar fourteen-character control head only uses an external speaker. With an internal speaker and basic control head, two different audio outputs can be selected. (Without the install manual for reference, I seem to recall there is a ten watt difference. The internal speaker is four watts audio output, and the external speaker, fourteen watts.)