Engine temperature gauge has no power to sending unit.

Attached is what I found on checking the gauge from my E Books purchase, but I want to check here first before I tear the dash apart. I checked the connector at the sending unit with a 12V test light. I checked the light on the battery before checking the plug at the sending unit. Plug has no power in either wire. The fuel, amp & oil pressure gauges are working as they should so I figure fuse box fuse #11 15A Gauges & Warning Lights is good. I didn't find anything related to this when I searched the forum.  ( On the E book purchase, I wouldn't buy it again).

Your EFI engine has both a sender and a sensor. (ECT)
The sensor is two wire and tells the computer to richen the mixture of a cold engine.

The sender is single wire and grounds the gauge with variable resistance so the needle moves.
With a good meter you should see approximately 5.5V pulsing on this wire.
Ground the (#39 R/W) wire and the gauge should full temp (don't do this for long or you will damage the instrument)

You should familiarize yourself with the 1985 EVTM (Electrical and Vacuum Troubleshooting Manual)
It can be found under Documentation/Electrical/EVTM/1985 EVTM.  https://www.garysgaragemahal.com/1985-evtm.html
You can usually find these used on eBay for ~$25 delivered.....

Thank you again. I forgot to check the auto notification box.

I have power to the sending unit. Now the problem is to id the correct sending unit. Mine has 2 wires but not a 2 wire listed for 1985? NOTE: the clips are broken off my plug. Maybe it's not making ood contact

As Jim said the 2 wire plug you pictured is for the EFI NOT the gauge.

The temp gauge is a single wire 90* rubber push on plug and as a guess is in the intake manifold.
Most of the time to the left (when in drivers seat) front top corner but could be wrong as you have EFI where do they put the temp sender?
Dave ----

Thanks Dave. I guess I didn't understand what Jim said. I'll keep searching. I did pull the starter and get the engine serial number. Wanted to make sure one of the PO's didn't do a swap.

That is not a "serial number".  It is a casting number.  And all you can tell from it is that it was cast in 1985 given the E5 in the number.

Thanks Gary. I'll keep looking to see if I can find any other numbers.

Found the sending unit.

Yep, that looks like the one.  

Gary Lewis wrote

Yep, that looks like the one.  

X2
Pull the wire and check with a test light it should blink if the wiring back to the gauge is good.
If you ground it, not long as you canhurt the gauge, the gauge should move if all is good like above.
If both above tests check good the sender is bad and needs to be replaced.
Dave ----

Thanks again Dave!

I replaced the sender as I was doin' other engine work. Gauge didn't work. Grounded wire, gauge didn't work. I have traced the wiring back to the firewall and didn't find any issues. I found a post in another forum that said there should be 5 volts in the wire. I used a safety pin to puncture the wire and checked wire in several placed. no voltage. I assume my next step is to remove the dash and check the printed circuit? Found this article on here:
gage cluster printed circuit repair/fix.

Ford instruments of this era go back to the day of 6V systems, essentially unchanged.
That would be Fuel, Coolant temp and Oil pressure.
The Instrument Cluster Voltage Regulator (ICVR) 'chops up' battery voltage and leves you with a ~5V average.
Gary was going to build one from scratch but found and implemented a solid state solution (SWAD-J)

If it's only the water temp instrument then you'll find the problem on the flex, or more likely in the plugs on the back of the cluster.

Enjoy your Thanksgiving holiday!

Thanks for the schoolin' Jim. Happy Turkey Day to you & yours!

As Jim said power (12v) comes in to the cluster going to the IVR then out to the 3 gauges (gas / temp / oil) and then out to each sender.

You have tested back to the firewall for power with no luck so you have to move on to the cluster.
As said look at the main plug as the copper strip on the printed board can come off and not make contact with the plug.

It can also be dirty I used some vary fine sand paper like 1200 grit.
I used it on all contacts for gauges, light sockets and the main plug.

If you use jumper wires and a 12 volt power you can bench test the cluster with a test light.
Power into the IVR and you should see the test light blink output of the IVR.
Following it more to each gauge you should have blinking light in and out of each gauge.

On the temp gauge if you have power in but none out of the gauge it would be bad in my book and need replacing.
If the temp gauge blinks on the output side follow it to the plug and see if you have power there.

At that point if the temp gauge has power (blinking) all the way back to the main plug you will need to check the temp wire from the plug back out to the sender to see where the fault is and repair it.

Short of doing it for you that is what needs to be done.
It could be once you have the cluster out and looking at the printed board you can see a bad spot and will need fining or me replacing it.
Dave ----

FuzzFace2 wrote

It can also be dirty I used some vary fine sand paper like 1200 grit.
I used it on all contacts for gauges, light sockets and the main plug.

 I've always used an ink/pen eraser, rubberized mild abrasive (similar to Craytex or Peco, the toy train track cleaner)

We used to be able to get the slip on ones that fit a pen like a pencil eraser but I don't know if they still exist.

Yep, I use an eraser as well.  But stay away from the end of the trace as you might snag it and peel the copper off the flex.

All the erasers I have are dried out and hard as a rock but yes eraser would work I just happen to have the 1200 grit paper.
Dave ----

Thanks Jim. Had to put up Christmas decorations this weekend so I'll go back to Big Red today.