Temperature Sensor Issues ( Temp gauge not responding)

[Sdude2008]

The new one came with what appeared to be a teflon coating on the threads. I’ll clean it off and go metal to metal. Thank you.

 

[RonD]

Yes, that is correct, the bottom few threads are bare metal that's enough, if the elbow has a good ground

Wait a minute...........................
At the bottom of the ad is say with TWO flat pins..........if it has 2 terminals then its the wrong one but you CAN add a ground wire to the extra pin
Just reading up on it, these should also ground thru the threads as well as the 2nd pin/terminal

 

[Sdude2008]

My old one had two pins so that’s what I got but maybe someone before me put the wrong one. I just cleaned out the threads and still nothing. I can connect the red wire to the batt neg and I get gauge. I grounded the brass base of the sender and nothing. I checked both pins with a test light and nothing. The only thing that gets gauge is plug off and grounding the red wire terminal. I notice every one on rockauto has two pins. I’ll get the two wire connector and splice it in and report back. Thank you.

 

[RonD]

Yes, they all have 2 terminals now

This really doesn't make any sense at all
Even if you could hook it up backwards it would just go to HOT same as grounding red wire

Do you have an OHM Meter?
To Test the old and new senders

This is what you should see: https://www.vintage-mustang.com/cdn...ang.com/attachments/1594607472514-png.761171/

10 ohms HOT
Direct ground is 0 ohms

So cold should be 78 or higher

 

[Sdude2008]

Two wire plug arrived today. I spliced the red wire and grounded the other wire to an intake bolt. Out for a drive now and still nothing. I’ll double check the ground but its the same place I grounded the red wire for the test.
Swapped wires and more nothing. Maybe I have the wrong sender…

 

[Sdude2008]

Decided to replace the thermostat and broke the brittle other temp sensor so… replaced the second sensor with the new one and put the original old gauge sender back. Now the gauge actually shows signs of life. This is the first reading Ive had since Ive owned it for ~5 yrs. Usually it’s dead below the lowest hash mark. This is after driving for ~25 min. I’m guessing the two pin ‘old’ sender might have come to life with the addition of the second ground wire. From what Ive been reading the temp reading could be accurate. It just seems so low from what Im used to in my other cars.
Any ideas?
Thank you.

<edit> Ron I saw your comments on another forum re this same issue. You mentioned the shapes and different voltages of the resistors in the sender vs the sensor. Maybe Im confised here too. I’m attaching a pic of the two parts that were in my truck since I bought it. The new sensors I see have the cone which mine does not. The black ‘sensor’ does not have a part number the gray ‘sender’ does. I have ordered the correct gray sender by part number. TIA

 

[Sdude2008]

Would you look at that. Replaced the sender with the correct part number and it works. Thanks to RonD for helping me realize someone had put a two pin sender in there and the solution was to add a second wire for ground. I appreciate your help Ron and the forum always. Now on to the next thing.