Temp Sensor 1971 Mustang 302

[folson]

Hey team hello have some issues understanding a Temp Light issue. The car has a Temp light (not Gauge) I have recently redid the entire cooling system. The light comes on almost Immediately when the car is running. Is this a indication that the sensor is Bad?

 

[tos]

Its more than likely bad but it depends, is it the original or did you replace it? the "dummy light" style works by completing a circuit when the temp reaches a certain degree. It works as a grounding point so internally it is open until that temp is reached then when it is then it will ground the circuit to complete it.
So another possibility is the wire is grounded somewhere else or something is miswired?

 

[folson]

Thanks Too! I knew its a simple symptom and fix but was worried that perhaps something else could cause it to come on so fast. Supposedly the motor was rebuilt before I got the car 71 Mustang base 302. So I am hoping that it s not a engine block issue.... I have a new sensor so I will be replacing today. By the way US Army retired.

 

[folson]

Hello Well I changed the sensor and no luck still comes on right away.... Any ideas where to look where it may be grounding out?

 

[tos]

There are a couple tests to do to get you started in the right direction.
First to intitially test for a ground you want to disconnect the wire from your sending unit. make sure it is not touching anything metal. start the car and see what it does. If the light comes on then you have eliminated the sending unit and have a possible ground.
Second, If the light does not come on then we need to test the sending unit because its either the wrong type or its defective. If made in china its not uncommon to get a few that are bad.
Get a multi meter and set it to ohms (with engine cool). Connect one wire to the top post (where the wire connects) on the sending unit and ground the other to the manifold or the body of the sending unit. If your ohm meter doesn't react then the sending unit is good. If it does react then you either have a bad sending unit or it is the type made for a gauge. If it is the type for a gauge then the ohms reading will change as it heats up. You can test it by letting the engine warm up and checking the readings as it warms up or you can pull the sending unit and warm it up with a cigarette lighter. If you have the wrong type then make sure whoever you are buying from knows its for a dummy light not gauge. Take a multimeter to the autoparts store and test it on the spot if that's where you are getting your sending unit.

 

[folson]

Thank You... Got it... It was a wrong sensor I believe. The sensor test worked and the temp light is not coming on. So I am pretty sure it was the sensor. I did add a better ground dash also and changed the voltage reg for the dash.