I have a KDC 319 Kenwood head unit in my car. I bought a cable that is supposed to connect an IPOD or smart phone with a headset jack (13 pin to headset and IPOD jack). I installed the cable but I cant set the unit to Aux. ???

SOURCE: Kenwood KDC-319 code needed

try this one KCAR

SOURCE: aux location

There is a RCA cable that comes off the back of the radio and also another cable for 3.5mm (mini-stereo jack) that also comes off the back of the radio. The RCA jacks can be used for "AUX" or "Sub-woofer" and the 3.5mm jack is just for "AUX". Your ipod can use the audio output jack or the headphone jack and plug that into the 3.5 mm jack on the back of the radio. You will need a "3.5mm male" to "3.5mm male" stereo cord that can be purchased at Radio Shack or Best Buy. Then you select "AUX" on the display with the source button to listen to it. You may need to go into the menu and activate the "AUX" input. Check your owners manual for details.

SOURCE: turn aux on on kenwood kdc-mp205

In order to access the AUX option the stereo needs to be in Standby mode. To do this just hit the SRC or source button until you reach the Standby option. Now hit the menu button and scroll up or down until you reach the AUX on/off option and just turn it on. Hope you find this helpful.

SOURCE: ipos nano 3

It will work bu tonly after enabling the aux jack.
Place unit in standby mode then press menu for a second and then goto aux and select it to aux on1

SOURCE: aux problem

You have to go into the standby menu and turn aux on. Go to standby, push menu button and scroll down to aux and turn on