Mystery Stereo Button Options

[cooneyc4]

Hi There,

I have had a 1994 gen 6 for the last 6 years and there is one button on the stereo that I can't figure out. The car is a japanese import with the original double din CD/Tape/Radio. The button has some arcs on it going from small to big something like this )))). When you press the button there is a buzzing sound from the speakers and the display says 1600, no other button does anything while this is on and you need to press it again to clear it.

I hope someone can help, as after 6 years I know the car inside and out.................except for the mystery button........