98 radio harness

I recently purchased a 1998 Galant ES. When I got it, it had recently been relieved of it's power radio antenna (the day i drove it off the lot). Since then I figured that I could take care of that in the future, but in the mean time I have wanted to play a few cd's not getting radio stations. I have a sony head unit that I had gotten a few years ago, and upgraded the harnesses for it to fit the galant. The only problem is that there is a round plug on the back of the factory head unit. One source says that it is for the factory amp. another says that it is for the factory cd changer. anyone know of a diagram, or detailed picture that I might get a little reference from?

It's more than likely for a factory CD changer. The amplifier (if the car has one), would more than likely be located under the passanger front seat and is powered up through the existing factory wiring harness. Make sure to hook up the sony's blue/white lead to the blue lead on the aftermarket harness. That way, you're all set when you get the new power antenna, and it'll turn on the amp if the car has one. Either way, you shouldn't have to worry about the round plug.