1998 Mercury Mountaineer CD player loses power

By combination switch, I am assuming you are refering to the multifunction switch on the steering column. I need to explaine a couple things. First, the CD player requires more power than the radio. Thus, it has a seperate power supply and an additional ground. What could be happening is while you worked on the switch, you may have loostened a body ground under the dash. Now, what can happen is this. Electric will always find the easiest way out. In other words, if there is a weak ground or another circuit it can ground through easier, it will go to the other circuit. Thus, electric will pass through something like a light, chime. And triger it to find the easier ground.

Overall, I feel you disrupted a ground circuit and that is what is causing the chime to go off at times and the CD player to not work at times. Check for loose, damaged or disconnected ground straps under the dash. Also, if you can, remove the stereo and run an additional ground from the radio's chassis to a good solid ground under the dash.

Nothing specific in that area. However, (and I hate to say it) you may want to remove the shroud and double check all connections. Also, check to make sure the ignition switch wasn't distrubed. As far as the CD player, just for the heck of it, run an additional ground to the chassis of the radio, and take a look under the dash to make sure nothing has come disconnected. They use those clips for grounding to sheet metal. They move, come loose, come off. They can be a pain.