A 1990 Mustang turn signals defroster and heater stopped working and the fuse is good where is the fuse in the engine located?

Each of those systems has it's OWN FUSE. Replace ALL of the affected system fuses with the proper size fuse in the correct fuse holder position, which is under the dashboard.

For a proper fuse diagram, go to a Ford dealer, in the parts dept ask for a photocopy of the fuse chart, and give the guy five bucks for his time and trouble, then buy the proper Ford fuses while you are there.

Further ideas. The heater and defroster have an electric motor that moves the air, is the motor burned out? Need to check that, too.

Turn signals, need a working flasher unit, to work properly, as well as four working turn signal bulbs. Check the flasher unit, located under the dash, silver round thingy with prongs that go into the fuse block, left side under dash. Check the turn signal and brake light bulbs, for proper operation , too.

Sounds like the ignition switch is coming a

part. pull the lower colum trim to see the switch. they separate where the plastic joins the metal. you can push it back together and bend the tabs back to secure it or replace the switch.