Temperature gauge not working

[NIGERIAN RANGER]

I have tried to diagnose why the temperature gauge on my truck isn't working.
Pls can anyone point me to the right direction here on troubleshooting?
There are two switches or temperature sensor or sender units on this truck I think. Which of them should I replace?

 

[kaltertod]

The Sender is the single wire unit in the thermostat housing That is what sends the temp signal to the guage. The other one is for the ecm only. Alot of times you can clean the post on the sender and use a pair of pliers to squeeze the connection so it is tighter and that is enough to make the gauge work.

 

[NIGERIAN RANGER]

Would try that then, thank

The Sender is the single wire unit in the thermostat housing That is what sends the temp signal to the guage. The other one is for the ecm only. Alot of times you can clean the post on the sender and use a pair of pliers to squeeze the connection so it is tighter and that is enough to make the gauge work.

Would try that this week. Thanks alot