I have a 96 safari that the heater switch only works on med-hi. I replaced the switch and the electrical device by the heater core(don't remember what it is called) and still the same. Any other options?

Check the blower relay and blower resistor array. You'll need a voltmeter and leads to back-probe the connectors while the blower is still in the circuit, or you may get false readings from the resistor array.