i know i need a usbc brick to charge my iphone 13 but can i use my old usb cord to connect to my car?

Yes. You can also use it to connect to an old USB power adapter if you have one. See the following from https://www.apple.com/iphone-13/

As part of our efforts to reach our environmental goals, iPhone 13 and iPhone 13 mini do not include a power adapter or EarPods. Included in the box is a USB‑C to Lightning Cable that supports fast charging and is compatible with USB‑C power adapters and computer ports.

We encourage you to re‑use your current USB‑A to Lightning cables, power adapters, and headphones, which are compatible with these iPhone models. But if you need any new Apple power adapters or headphones, they are available for purchase.