Hi Hans,
Happy to help you out with your paint rectification/correction questions here.
Sorry, but the news is not going to be all that good for you. First up, what are your expectations for a final result, on improving the overall appearance of this car? That's important, as you will find there will be not much you can do to greatly improve the look from what the car is now. How so? Let's get technical, and dive right into it to explain what i mean.
I could waffle on for hours, deep diving into all the technical details, products and techniques on paint restoration/ correction, which would be of some help for you (steps 1 to 1000), but looking at your photo shows what you are confronted with here, which presents bigger problems for you to address.
Your car is just over 50 years old. Would you believe 50 year old original factory paint can still be in very good condition if the car was babied and kept out of the sun all its life. My '73 Vert is living proof of that. The factory color is Gold Glow Metallic, and still has the original factory paint from the front doors back to the tail lights in excellent condition. UV sun exposure and uv sun damage is the number one enemy of any paint film for any car. The more exposure the car has to the sun, the greater the paint damage will be. So, looking at your photo of your Mustang, we see that the paint has oxidized fairly badly all over the car. The lower sides appear not to have oxidized as badly as all the horizontal surfaces, such as roof, trunk and hood. This is typical of most sun damaged cars. Also, when people say their paintwork is faded, it refers to the (color only) of the car fading to a lighter appearance due to uv sun damage. In your case we notice mainly a bad dulling off of the paintwork. This is called oxidation of the paint finish.
The obvious solution to help restore or rectify an oxidized paint film is to determine how badly sun damaged the paint is. It goes that the more oxidized a paint film is, the less chance you will have in bringing the gloss level back to a decent appearance. There is a cross over point here, if the paint film has oxidized too badly, it will mean that it can't be restored with any cut an polishing attempt at all. The weapon of choice generally to cut back the oxidized paint film, is a rotary buffer/ polisher using a lambswool bonnet or a foam pad teamed with a good quality 2 pack cutting compound such as the Farecla brand cutter. However, we notice that your hood has suffered paint damage, that will need to be resprayed/ refinished, as the paint is too far gone for any attempt at correction. That would also mean refinishing the two front fenders as well, as the metallic color would need to be back blended into the tops of the two front fenders, and then the whole of the fenders finished in a clean clear as well.
That all said, here's where the news gets bad for you. Your car started with it's original factory paint. During it's lifetime, we don't know if any of the car panels have been refinished or resprayed later on down the track. To explain, the main problem with any factory metallic color from 1971 to 1973, was that the cars were factory shot with what was called a mono metallic paint. A mono enamel paint was where the metallic color and the clean clear were mixed in together, and then sprayed onto the cars in one go. I used to spray cars with the mono enamel paints back in the mid Seventies when i was serving my apprenticeship days in the trade. The move to two stage /two pack paints took off in the late Seventies, making the use of mono enamels a setting sun very quickly. Today's cars are two staged sprayed with a colored base coat and then a clean clear 2k top coat. But the major problem with the old mono metallic enamels, is they cannot be successfully cut and polished back, at any stage. As soon as you attempt to cut and polish a mono enamel paint film, you get a problem call shedding. Shedding is where you are exposing the raw aluminium flakes by cutting back into the paint film. This produces an unwanted appearance of an uneven/ mottle type look, and as well, you cannot achieve a decent glossy appearance. The more you cut and polish the paint film, the worse this condition gets. In my case, i experienced the exact same problem with my '73 Vert. I can't cut and polish my own car, as i get the same thing happening, even though my paint work is still in great condition. Even hand polishing with a non abrasive polish will produce a shedding problem as well for me. You can see all the black aluminium that has shedded on your buff pad or hand polish rag.
However, if your car has been partly or wholly refinished at some stage with a base coat / clear coat system, then you could move in and try the cut and polish method to help restore the oxidization problem you have. If you have still got the mono enamel finish on your car, then sorry there is little you can do to correct the paint film. There is nothing much you can do at all to restore any metallic sun damaged mono enamel i'm afraid. If for example, your expectations are fairly high for the cars final upgraded appearance, then you really need to be thinking about a complete respray, going by the photo you have provided.
Finally, i have included a link here for the main benefit of the Forum members regarding some good technical feedback and help on paint finish problems, and paint correction techniques/ problem solving solutions. It makes for a good read!
https://www.ocdcarcare.com/auto-detailing-articles/common-auto-detailing-paint-defects/
Hope all that helps,
Greg. (Pro Auto Spray painter)
