Stock '06 Lucerne head unit with small round audio input at lower right corner. Not a usb port. Manual states that an ipod can be plugged into that- what cable is needed?

Vehicle is new to me, and I thought maybe someone here can help point me to the solution. Not sure what I need and where to look.

What is the model # of ipod that you have?
The jack you are describing at car deck is called a 3.5mm male.
The ipod headphone output should be the same size, 3.5mm.
This cable type of 2 male 3.5mm should connect.

You also may be able to connect via bluetooth if your car deck and ipod is capable.

Excellent. Thank you for taking the time to post up the answer.

This is a good one from Amazon, is has a step-down design on the plug, so it is supposed to fit the i-phone more snug.
It gets really good ratings also, over 6k reviews.