How do you fix the heater in a 1984 Toyota Tercel?

When you turn on the heater switch does nothing at all happen ? This coule be because the heater swith cable that goes to the water pipes and turns a switch to allow war water to flow has snapped, an easy fix is to find this switch (Should be around the back of the engine or on the bulkhead) and switch it so it is on allow hot water flow all the time when warmet weather comes switch it back to allow air con/ cold air.