You didn't really give enough info....
Which particular CD6 radio is it?
Does it have an "AUX" button on the radio's front panel?
Do you have a 3.5 mm stereo audio input (ie, mini-headphone) jack somewhere below the radio, say, down near the truck's ash tray?
How many, and which style of electrical connectors are on the back of the radio (ignoring the antenna)?
Do you have anything plugged into them?
If you happen to have an AUX button, and your radio has connectors on the back, except your vehicle has no AUX jack, then perhaps you can add one, and mount it anywhere. That's what I did, seen here: Ford Ranger 2008 Radio - Imgur