will I have problems bringing a car headlight as carry-on flying US Airways flight?
The link you give states it's 29" long. That's a lot longer than the standard carry on and might get turned away. If its boxed the dimensions will probably be even bigger. If you can carry it on hopefully you're in a high boarding group because its going to take up a lot of overhead space. On the Express flight it probably won't be allowed as carry on as those bins are much smaller on some a/c.