Sounds like either the plug or the radiator need replaced.
Bottom of radiator.
The 1999 Wrangler is equipped with an overflow tank. The amount iof coolant to add to the radiator is slightly less than 2 gallons. Be sure to use either a 50/50 coolant (pre-mixed with water) or a gallon of concentrated coolant mixed with an equal amount of water. You will have about 3/4 inch of coolant left in the container when the radiator is full. The overflow tank is there to hold coolant when the radiator gets warm and needs to expell some of the coolant. So just fill the radiator with coolant. You'll know when it's full.
Lower passenger side of radiator, motor side.
Best thing to do is use the all models safe coolant, it covers all the bases
It should be on the passenger side next to the radiator.
It is in the passenger side coolant tank on the radiator. If the light is on and the coolant is at the proper level then the sensor is defective. To replace it you will have to drain the radiator. Disconnect the wire and remove the clip and remove the sensor.
The radiator drain plug should be located on the bottom of the radiator on the passenger side. Open that, let the old coolant flow into a drain pan, replace the drain plug once the coolant is out and the radiator is flushed, then fill it up through the radiator cap.
The windshield streaming after a radiator change on a 1993 Jeep Wrangler is a result of a loose connection. Steam is caused when coolant leaks onto the engine and is heated rapidly.
Right on the thermostat housing, follow the upper radiator hose to the motor and there it is.
Fill the radiator through the coolant resivour, which is on the passenger side engine compartment.
The radiator cap is on the coolant reservoir, which is mounted on the passenger side fender for S series Saturns.
There's a drain plug on the bottom passenger side of the radiator. Unscrew it and the coolant will drain.