1993 Ford Ranger Heater core

When you say no heat, do you mean you have air blowing but it's not warm, or you don't have air at all?

If you do have air coming out, make sure the heater core is the culprit for your no heat problem:
with car at normal operating temperature and heat set on high, feel both inlet and outlet heater hoses under the hood. They should both feel hot. If one feels cold or much colder than the other, then your heater core is defective. But if they're both very hot, your heater core is probably fine.
Have you checked your level of coolant? add some coolant if it's too low.
Also, can you hear the blend door moving inside your dash when you move the temp control?

Your heater core is located behind the glove box inside the plenum. just drop the glove box, and unscrew the plenum cover, and your heater core should be right behind. replacing the heater core on this year/model is an easy job.