Jensen JWM990 Installation And Operation Manual page 9

Speaker Output
The three speaker output buttons (A SPEAKER (27), B SPEAKER (28) and C SPEAKER (29))
control speaker output from the radio. Press any of the three buttons to turn the corresponding
speaker sets on or off. SPK A, SPK B or SPK C will appear on the display.
Reset
The reset button should be activated for the following reasons:

initial installation of the unit when all wiring is completed

function buttons do not operate

error symbol on the display
Use a ball point pen or thin metal object to press the reset button (16).
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JWM990