Ground Problem When using Cig Adaptor with AUX? Help

[mattk22]

I have been having problems with my AUX jack not working with my external Sirius unit, it would work in AUX mode for a little then it would kick back to radio and not go back to AUX until I unplugged my Sirius unit. Well the other day I was in the car and my iPod was running low on battery and I plugged an iPod power cord into the Cig lighter and the radio kicked off AUX and back to radio. Is it some kind of grounding problem with the Cig lighter and the AUX jack? Why would this happen and how do I fix it? Thanks!