Hi, ponygirl and welcome to the site. You have a very nice looking Mustang. Welcome to the site, and come back often. Now, as far as your rollbar light, are you sure you have a factory installed rollbar? If so, are you sure you have a light on it, because normally rollbars do not have lights. However, if it does have a light, first check to see if the bulb is good, then use a multi meter to check if voltage is present at the receptacle. If not, then check all your fuses. Secondly, you can get original equipment (OEM) tail lights at any Ford company. Thirdly, your timing is off for the altitude you are running that pony if it is pinging. If you don't know how to adjust your timing, then take it to a Ford dealer. They have fancy and expensive equipment to check your computer.
Again, welcome aboard.