Does anyone know how to track power the lights in the old style passenger cars?

You have to purchase the wipers on the Bachmann parts store website.
You'll need two sets of these per car :
https://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=69_75&products_id=649Of
 iI your car doesn't have metal wheels on the trucks, you'll need to buy two of these per car:
https://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=69_75&products_id=581
And then you'll have to disassemble the cars to run the wires.
Mike

There has to be an easier way to do this. Why do you have to take the whole car apart?

If you want to power your cars via track power, you'll have to get inside of them and do some very simple, easy wiring connections.
It's not hard.
In fact, it's a very simple and easy process.
If you're not willing to do the simple work, then don't.
Stick to the 9v batteries.
I don't have time to walk you through what is a simple, and fairly easy project.
I've done over a dozen of these Bachmann cars.
And several from other manufacturers that I can't name here.
Do you think that I knew how to do the job from the get go ?
No.
I disassembled the cars and figured it out on my own.
I even figured out how to change the original incandescent bulbs out for  5MM Warm White LED's.
I added capacitors and bridge rectifiers so that the lights don't flicker(what the capacitor is needed for),and bridge rectifiers(for the polarity change) so that the lights stay on when the cars are going both forwards as well as reverse.
LED's only work when the current is flowing in a forward direction.
And that's what you need to do.
Here's a video showing some of my lighting work
Note that every car on both trains has had track powered lighting added by yours truly:
https://www.youtube.com/watch?v=WIVpc0aSktc&t=11s
Good luck!