either the raly or the temperatuyre sensor is having an electrical system. They should not be too hard to replace. Have the relay tested, then try the sensor. The temp sensor located on the driverside right next to the plugs on the block.
The year says it all. That sensor it a goner. Why dont you flush the radiator, replace the thermostat and sensor? Your better of that way. Also check the water pump if its not leaking.