Hi, I got a car radio Kenwood "KRC-757". On the front panel there is a button labeled "direct". When I press it, the LCD screen displays "1888", then it returns to the normal frequency display of radio station. I don't understant the function of "direct". Is it the auxiliary input, or anything else? There is a pre-output level select switch under the chassis. One is 300mV, the high level is 1V. I connect it to my amp and find the output level could change when I adjust the volume. I wonder if the previous owner modified the radio. Thanks in advance.