Why does the catalytic co nverters on a 1989 ford mustang turn red?

There are two main possible answers to this question. The purpose of the Catalytic converter is to burn excess fuel before entering the atmosphere, it does this through a honey comb that gets hot. If the car is running rich (Performance related, Air cleaner dirty, Injectors warn or ??) can cause the honey comb to melt and plug which in-turn will cause it to glow red. Secondly, if the car is used on very short runs, the cat will collect carbon, plug up and glow. Usually, if the cat is glowing noticeably red, you should notice power loss especially at high speeds. Some can be taken apart and cleaned, others have to be replaced.