1986 F150 Temperature Gage Not Wroking

[dxt7339]

I have a 1986 F150, 4.9L , Manual transmission. The Temperature Gage is not reading. The IVR on the instrument cluster is working. Steady voltage on one terminal and pulsing on the other terminal. The Coolant temperature sensor is at the thermostat housing outlet. It is a TWO (2) wire temperature sensor. There is a Black with white stripe wire and a green wire at the connection to the sensor. The sensor has continuity across the two contact pins and when cold it is about 65 ohms and hot it is about 4.5 ohms. The wire at the instrument cluster connection block that feeds the temperature gage is a red with white stripe. The gage itself has continuity across the two terminals and reads about 12.6 ohms.

All the wiring diagrams that I have found on the internet that seem to be for this model truck only show a single wire, Red with white stripe, going straight to the temperature gage.
With the key on, there is 9.5 volts on each of the wires at the temperature sensor which is very confusing.

I need some help figuring this out.

Thanks!

 

[Fellro]

That is not the sensor for the gauge. It is on the passenger side in the block towards the rear of the engine. I had to change mine a while back. Not the greatest place to get to, but ends up not being as bad as it looks. It does have a single wire to it.

 

[dxt7339]

Thanks for this information! I can barely see it now from the top/front of the engine. Do you have any suggestions/tricks that you learned getting to this sensor? It looks like a real pain!

Thanks!

 

[Fellro]

It actually isn't quite as bad as it looks, but is definitely a messy job. I did it from the top side. I had to do it on an 88.

 

[dxt7339]

Wow! doi ng it from the top side looked to be very difficult. I decided to go from the bottom and remove the starter. After that, not too bad a reach. It would have been a 30 minute job, but the aftermarket temperature sneson had a larger size terminal stud and my connection would not just slide on like the original, so I had to make a little adapter and the terminal stud is not SAE, but 5 mm metric, which I had to go get some 5 mm nuts and washers. But I got it done and the gage is working properly now!

Thanks for your reply!

 

[Fellro]

It's been a couple years so don't fully remember how I did it, but don't recall doing it that way.