Trying to find schematics that show how the coolant temp sensor sends its info to both the controller and the gauge.

 

The "coolant temperature sender" -single wire- is wired to the gauge in the dash. The "engine coolant temperature sensor" -2 wires- is wired to the ECA.

 

Single unit with 3 wires? If yes, then one should be signal to PCM (prob LT Green/red), one should be a signal return (ground) for PCM (probably gray-red), and the third should be a variable resistance to case ground for the guage. (unsure of color). The two for the PCM should show a resistance between them that varies with temp, while the gauge lead should have some resistance between it and the engine ground that also varies with temp. With the connector unplugged, two should show no continuity to ground but should to each other. These are the PCM leads. Not sure what year you are dealing with, so it could be different, but this applies to most of the 90's. If it's newer or older than that, Franklin2 can probably answer any questions. He's really sharp on electrical systems.
Jim

 

Many thanks to you folks for the help; my vehicle is an '88 F250, 351W. (sorry) I've got wires all over the place, trying to trace this problem down, i.e. (it's a two-wire sensor) does the (useable) signal split off, one to the controller, the other to the gauge? or into the controller, then back out again........anyone know what color it might be at the firewall feedthru?

 

87xlt was correct. But I guess he didn't make it clear that there are two seperate sensors. The one with two wires goes to the computer, the one with one wire goes to the guage. It does not split off or share duties with one sensor. I will see if I can find the wire colors.

 

more info: from the wiring diagrams I do have, I've pinned out the harness from the ECT sensor to the computer's connector, and good continuity. I've also found a red/white wire at the firewall feed thru that deflected the gauge towards H and stayed there when I shot a very low V thru it. Turning the key to run sent it back to under C. I am getting closer....my little hands are physically checking the harness for ........well, I'm not sure, but hopefully I'll know it when I see it.
Specifically, do you (all) mean that I'm equipped with two sensors that measure coolant temp? one with two wires that feeds info to the computer and one that feeds info to the gauge? Even though that makes some sense, I'll be stumped to find the 'other' one......hehehehe thanks to all of you for your help!