4runner heater problem

have a 1990 toyota 4runner SR5 3.0 V6 with an automatic transmission. I am having a problem with the heater. The fan blows, but the air is barely warm. The radiator is full and the engine warms up fine. I think the problem is in the heater control. I found the box and the wire that connects to the dashboard temperature control slide. The clip on the wire was off so I kinda' pushed the wire in and re clipped it. Now the heater is working a little better but still not like it should. Do I need to take something off and readjust the control wire?
rimshot

Thermostat maybe? does the engine temp gauge seem very low (aka 1/4) Its suppsoed to be at 1/2 most of the time.

Replace the thermostat would be my suggestion.