power pack overload comes on

[A Trainman]

gooner_1967,

I know this sounds simple but... did you try the, little, slide switch, on the bottom, near the battery compartment?
Also how many passenger cars do you have? Do they all not light up? Did any light up before?
If they all have a battery compartment than, most likely, they all are lighted by battery power not track power. Also look at the wheel sets to see if there are any "pickups" or wires connected that would use track power to light the cars. If no wires (on the trucks) then you should check and make sure the battery connections are good and clean. also the 9v battery should fit in only one direction, it could possibly be installed with the positive and negative reversed. That wouldn't make the lights not work but the connections may not mate up correctly.   
That's all the simple stuff. If none of this works it gets a little more complicated.
Give us all a heads up to what you find.

Adam
 

[gooner_1967]

adam i have 2 cars from the royal blue set,they both run the lights from a 9 volt battery and they worked before.when i moved few yrs ago,i put them in the garage on a metal stand.i got them out few days ago,put in a fresh battery,turn the switch on and nothing happen.i did just found out that when i sent the switch in a certain spot,the lights comes on,but only one comes on,not the other in both cars.so right now i just one light from the cars,the back light also comes on,but only one light inside.i think both swiches has some kind of short in them.like i said,if i set the swiches at a certain spot,they work

[A Trainman]

gooner_1967,

Sounds like you figured out the problem, good job! Bad switch, try working it back and forth awhile.
If you live in a humid area, corrosion could form on the switch contacts and also the contacts for the bulb, especially if you left them stored with batteries installed. (electrolysis) If I'm remembering correctly the bulbs in the passenger cars screw in just like a regular light bulb.
I've used an electrical contact cleaner, "tuner cleaner" purchased from Radio Shack, to clean and protect switch contacts in the past. You might try that if you can find an open Radio Shack or electronics supply store, just make certain it's plastic compatible!
If you're not mechanically inclined, you might want to see if you can find a garden railroad club in your area to help you out. Or, you could also call the Bachmann Service Department to see what they would charge to repair your cars. I had a great experience with them in the past.
It sounds like you're on the right track. (no pun intended)
Let us know what you find.

Adam