Why won't your 1985 Ford Mustang LX 50 start when engine is hot?

Unfortunately, it could be any number of things. Electronic components often fail when they are hot but function perfectly when cold. Fuel delivery systems often react differently when hot than they do when cold. I always advise people to look to the basics if an engine isn't running at all: fuel, ignition and compression. Make certain that the engine is getting fuel. A quick test can be to shoot a little starter fluid in the intake while an assistant cranks the engine when it refuses to start. If it only runs while starter fluid is being introduced, you have a fuel problem. Pull a sparkplug wire, put an old sparkplug on the end and set it on the block somewhere. Crank the engine when it refuses to start and watch to see if the sparkplug has a spark. If not, you probably have a problem with the electronics. All you can do is narrow it down a little at a time like that. Good luck.