Not so much providing, but having a voltage there so a ground will be evident to it. Like door switches, they have to have voltage so the computers can sense when the switch grounds it out. I haven't had to rewire one, I am just throwing out ideas to be helpful.

 

So checking the voltage of the thermocouple leads I find:

key off, engine somewhat warm from last trial, voltmeter on 2 V scale
yellow .04 volts
red .04 volts

at idle
yellow .024 v
red .019 v

at 30 mph
yellow .034 v
red .028 v

key off again
yellow .053 v
red .048 v

If that's any help?

 

No. I meant providing. A door switch simply allows voltage applied on one wire to flow through to the other wire. A thermocouple uses the Thermoelectric effect to convert heat energy into electrical energy. The gauge measures this electricity.

Take a thermocouple probe and attach your multi-meter, set to read low DC voltage, to the probe's wires and you should see a current. The hotter the probe, the more current.

 

It doesn't seem like it. 0.001-0.006v difference isn't enough differentiate the temperature. That is probably just induced voltage. I think yours is going to be resistive, so you will need a source voltage.

 

I'm assuming you are measuring the voltage between each wire and ground individually. Try measuring the voltage between each wire. Meaning, touch one of your meters probe to one wire and the other probe to the other wire.

The voltages will be rather low. I've been trying to find some information somewhere on what voltages to expect but I haven't found anything yet.

On Edit: Here is what I was looking for. Voltage tables for type K thermocouples. Note the voltages are in milliVolts. So there is a very tiny amount of voltage produced for a given temperature.
http://www.pyromation.com/downloads/data/emfk_f.pdf

 

dchamberlain

Now that's making sense to me!

voltmeter set to 200m scale:

key off, engine just warm 1.00 v (edit: I mean millivolts)

at 30 mph 8.10 v

engine off again 6.10 v

On the table you sent the link for, 8.1 millivolts would be around 390 degrees F which sounds reasonable to me for cruising with no load other than the truck itself.

The voltage climbs and falls rapidly with load on the engine which is exactly what the pyrometer in my last truck did - pulling a trailer up hill or accelerating quickly it climbs very fast, cruising it holds steady, coasting it drops quickly.

So it's simple, the gauge just takes that info, and turns the needle accordingly, using 12v power to drive the needle.

With pos. lead attached to yellow and neg. lead to red the numbers were positive, connecting pos. to red and neg, to yellow the numbers were negative.

So if the two pins (#1 & #6) are there to receive this information from the thermocouple then it does makes sense that they are neither ground nor powered?

And if so the catch 22 question is of course yellow over red or red over yellow?

If I have to pick I will go red over yellow. And the very low voltage not harming the gauge makes sense to me. Especially if all it is likely to do is move the needle backwards and I can disconnect pretty fast.

Thanks for the excellent ideas!

 

Yeah, it sounds like you're on the right track. The two pins, #1 and #6, are there to measure the voltage, so it would make sense that they have no voltage on them, nor are they ground.

I wish I had more information on which way to put them, or if there was any chance of harm if you put them in wrong, though.

 

So I got brave and tried pins 1 & 6

Tried red over yellow and yellow over red and neither did anything.

The gauge reads 270 with the key off. When you turn to run it drops fast to 0 then jumps up to 270 again. (self calibration according to Autometer).

With the ends back in the plastic connector (they come out easy, no wonder I had trouble, should have been more careful) and the connector plugged in the needle drops to 0, jumps to 270 and sits.

So that which made sense to me did not get me anywhere.

Where's that drawing board gone...

 

Reax & dchamberlain

Thanks for all your help with this!

I called Autometer Tech Service this morning. Fellow I talked to knew right away what I was asking. I told him I pulled out some wires when fishing the connector through the A pillar, his first question was "just the thermocouple wires or all the wires?

I told him just the two from the thermocouple and he immediately said "the red goes under the other red" (so that would be hole #5 on the bottom as I numbered them, one of the 2.48 v pins when the gauge is powered) and "the yellow goes under the black" (which would be #3 hole on the bottom, next to the white). That he was able to answer instantly was interesting to me.

So I got home tonight and tried it - red under red, yellow under black. Turn the key to run, the needle drops from 270 to 0 then spins instantly all the way to 1600 (to the stop at the top end). Unplug the yellow the needle stays at 1600. Turn the key to off then back to run the needle drops to 0, turns to 450 and sits. Plug the yellow back in, spins to 1600 and sits.

So, I say to myself, obviously red under red and yellow under black is not correct or the gauge is fried.

I turn the key off and move the yellow to hole #4 on the bottom, leaving red under red in hole #5 on the bottom - this would be then wires in both holes that showed 2.48 v with the gauge powered up. Turn the key to run, needle drops to 0, turns to about 300 and sits. Thinking I might as well go all the way now so I start the truck and the needle begins to slowly climb to about 350.

Thinking that this just might be it I go for a drive around the block. Semi-hard acceleration the needle climbs smoothly to 700 - 800, crusing along at 30 mph it drops back to 500 or so. Step on the pedal it moves up as it seems it should, let off the fuel it drops smoothly back down.

I think I got it! Obviously I need to go for a longer drive and pull the trailer to see what it runs up to but it seems right.

Would you have any idea of what "normal" EGT's would be in your trucks?

Anyway and again, thanks for all your help. If the Tech Service was open Saturday you would have missed my adventure, if they were open now I would have called again about the yellow under black not working. If the guy had not answered so readily I would have got into the explanation about which pins were grounds, which had 2.48 v, etc. Seemed he knew exactly my issue so I hung up too fast.

Sorry to go on so long.

 

I'm a bit surprised that the thermocouple pins appear to have some voltage. But it appears that you have it working.

I have an Edge Evolution that displays PID data such as engine/oil temp, boost, etc. It has a thermocouple attached so that it can read EGT. It shows all these numbers digitally.

At key on with a cold engine it reads somewhere pretty near ambient temp. At idle, it runs in the neighborhood of 300 degree's. Flat level driving at 55/60 I run in the 5-600 degree area. An almost imperceptible climb can raise it 1-200 degree's and similarly a minor descent can drop it 1-200 degree's.

Climbing an average hill at highway speed will get me up around 800 or so, and similarly, going down an average hill can drop it down to 300 or less.

Climbing the Willamette pass, 6% grade, in 4th (I have the manual transmission) at 60mph, carrying a 3000 pound slide in camper, will run it up around 1100 or so. I don't know exactly what the "redline" is, but the Edge has an alert function to alert me to high conditions (overtemp, etc) and the default alert for EGT is 1250.

These are the my best recollection anyway.