I have a 1987 mustang GT - the temperature gauge needle does not move from the bottom or cold possition. I tried testing the sensor to ground no change in needle position. when i turn the light switch on all of the gauges light - any suggestions

Wrong gauge for the sensor? Bad gauge?

faulty sensor or a damaged wire to the sensor

check temp sensor by thermostat

Could be the coolant temp sensor:



4.0L engine shown





5.2L engine shown



To test it:

Perform this test on a cold or cool engine.

1. Disconnect the negative (-) battery cable.
   
2. Unplug the electrical wiring from the sending unit.
   
3. Using an ohmmeter, measure the resistance between the terminal and the sending unit's metal body
   
   1. Infinite resistance or zero resistance: the sending unit is bad, replace the sender with a new one.
      
   2. Other than infinite or zero resistance: continue test.
      
4. Remove the temperature sender from the engine.
   
5. Position the sending unit so the metal shaft (opposite end from the electrical connectors) is in a pot of water. Make sure that the electrical connector is not submerged and only the tip of the sending unit's body is in the water.
   
6. Heat the pot of water at a medium rate. While the water is warming, continue to measure the resistance of the terminal and the metal body of the sending unit:
   
   1. As the water warms up, the resistance goes down in a steady manner: the sending unit is good.
      
   2. As the water warms up, the resistance does not change or changes in erratic jumps: the sender is bad, replace it with a new one.
      
7. Install the good or new sending unit into the engine, then connect the negative battery cable.
   

1. With the engine cold, remove the ECT sensor.
   
2. Immerse the tip of the sensor in container of water.
   
3. Connect a digital ohmmeter to the two terminals of the sensor.
   
4. Using a calibrated thermometer, compare the resistance of the sensor to the temperature of the water. Refer to the sensor resistance illustration.
   
5. Repeat the test at two other temperature points, heating or cooling the water as necessary.
   
6. If the sensor does not meet specification, it must be replaced.
   

Submerge the end of the temperature sensor in cold or hot water and check resistance



Temperature-to-resistance relationship of the ECT and MAT sensors

Find the temperture sensor on the engine and see if it is connected, if it is then test to see if its working properly if not then its probably defective and you have to replace it.

Hi - sad to hear your having trouble with your Mustan.

Let me try to put you in the right direction.
Sometimes the gauges become magnetized because of variations in the quality of that gauge or some other anomaly.
Try this.
Before you start the engine and while it is cold, pull the temperature wire loose at the sending unit on the engine. See if this drops the needle to zero degrees. If it does - you will notice that even when the car is operating temperature the needle will still read zero. If you are sure the car isn't over heating - drive the car like this for a few trips to the store or to work and home. If you're not 100% sure the car is running fine be sure to stop and check that no water is escaping from the engine water hoses.
Hook the wire back up and see if that doesn't demagnetize the unit. I would save my pennies and either replace the sending unit - gauge or both.

I hope this helps you get your car back to where you want it.

Please rate me high if my advice has helped you.

Thanks
RICESKI

Hi. the vdc at the sensor seems to be fine. if the ground is sufficient, i would replace the gauge. its malfunctioning. Check for loose connection at gauge before replacing the gauge.

Your description of the problem is not very clear. It seems as if your temp gauge does not work, or does not indicate the correct temperature.
If you disconnect the wire from the sensor unit and put it to battery negative (ground), the gauge should move to the full hot position. If this does not happen the best chance is that the gauge does not work. If it does work, the sensor is faulty. In a very unlikely situation, the wire could be faulty..

what i used to do is pour a small bottle of rubbing alcohol in the gas tank....this mixture burns very hot so it will clean everything out thus burning all the gas particles off......i used to do this in a 1988 mustang gt that ran real rich because of performance parts and i couldnt ever get it to pass the tests....also try o2 sensors as well as possibly map sensor if equipped...this could be the problem....
temp gauge not working? check wiring and also check tempature sending unit and block temperature sensor.