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66 with gauge cluster. The temp gauge does not come off full cold when engine is operating. Before I conclude bad gauge and replace, is there a method to check the temp sending unit and the circuit? It is a 1 terminal connection at the temp sending unit.
Thanks for assist
HB

First ground the wire at the sender. Turn on the ign. The gauge should go all the way to hot. If so the gauge & circuit are probably ok. The sender can be tested but its easier & better to put in a new one. They are not expensive. Make sure you get one for a gauge & not a light.
George

Will give it a try George. Thanks.

Nothing. Shorted the sender circuit and no life in the gauge. The wiring harness is new. Is there a method to check the circuit to the gauge, before I have to struggle to take the gauge out.
2nd question - I have a spare gauge. Is there a method to check it before I struggle to install? Is it as simple as checking continuity across the poles?

Does the fuel gauge work? I'm pretty sure the same excitation circuit powers both the temp and fuel gauges.
Jerry

At least for me, it's important to know history. What happened. all was good, then one day, was not or.......... was good and after restoration work, was not.

When you took the wire off of the sender and shorted it to a good ground, what happened? I believe you said gauge did not respond. Did you try it with key on? If it did not go to hot, or near hot, then the gauge portion of the equation has a problem. This is where the first focus would be. So: Check the hot terminal on gauge to see 12V. Key on. No 12V?, no good, check fuse, wiring, ignition switch and etc. The gauge cluster is not too hard to remove and lay it upside down in the opening to test or remove gauge or entire cluster.

12V present at gauge? Then check continuity of the sender wire. Take wire off of sender and off of gauge for this test. Report findings.

Did temp gauge work before new harness?
Did gauge work after new harness until now?
Any other happenings? Other things not working?
Is sender new? is gauge new? What is the history of that pair working together?
Is this the 62 or 66? Is this truck supposed to have lights or a gauge?

66. Truck has been in resto for 18 months. Gauge cluster is new to me and I do not know of history. Dont have sense of these gauges. 62 has the lights, so I am working through the gauges and this is my first experience with them. Did clean things up prior to installing the cluster so I think gauge is finding good ground to cluster. I think I will test with a ground direct from gauge to cab to be sure. Sender is also new.
When we ran and tuned the engine, with Jerry's help, we got good temp health at the thermostat, radiator and through the block, so I think the engine is operating normally.
Ground sender circuit with ignition on and with truck running on a couple of different trys. Have not connected fuel gauge yet. Come to think of it the battery/amps gauge has not caught my attention other than it is in the middle. How do I test that to make it move?

I removed part about gauge being grounded. Now don't think it should be. Also rewrote some sections of my post. Sorry.

Sometimes a light compatible sender is used by mistake on a gauge circuit and may cause trouble. If sender has a single terminal, it is most likely a gauge sender. Two terminals, it's a light/annunciator sender. What motor is in the 66?

You say you took wire off of sender and touched that wire to a good ground on the motor or ran it over to negative battery , with key on, and gauge did not move off of cold. Is that correct?

You keep saying grounded "sender circuit", just want to be sure you grounded the loose wire to a ground spot. Key on. Motor does not need to be running. Just being sure our words are the same meaning and that test was done according to Hoyle/as Wrenchbender said.

Somehow you will have to perform the tests described in previous posts if grounding sender wire at motor end has no results.

As far as amp gauge, when key is first on you may see a jump. With motor on, it should go to middle or slight pos. When near middle, turn on high beams, should move toward minus and recover toward pos. Approximately. Rev may produce small movement to pos.

Thanks Bartamos. I am tracking with your suggestions. They are making sense to me.
Yes - 1 terminal sender. Bought as a gauge sender. 292. ((Also have a post running troubleshooting the hot lt on my 62. Hot Lt does not come on with key in start position during test. Good lt when I ground the terminal at the sender end so I know circuit and lt work.))
Yes - Took wire off the sender and grounded to neg at battery. Needle did not move from cold.
Yes - your description is what I did. I will check for continuity across the gauge and check 12v to the gauge.
Amp gauge - I will pay more attention to it. Lights and turn signals are not installed yet. If I disconnect the alternator wire with truck running the needle should move yes?

Disconnect that wire at your own risk- - - - -I've seen voltage spikes on an oscilloscope in excess of 100 volts just as the connection is broken. Solid state voltage regulators don't like those kinds of voltage transients. Simply turning high beam headlights on and off and/or running high current draw accessories like the heater blower with the engine not running should show ammeter needle deflections without putting your alternator in jeopardy.
Jerry

"I will check for continuity across the gauge and check 12v to the gauge."

I don't know anyone's knowledge, understanding and meaning of certain phrases so I am not disrespecting anyone. I need to be sure that I am stating clearly so as to help.

The method for troubleshooting the gauge, now that the first test shows no reaction at gauge, is to be sure gauge it is getting 12V. So that's one test. Using a test light at gauge terminal or a multimeter set to 20VDC. This identifies 12V problems, like blown fuse, bad connections, bad ignition switch or wiring mistakes. Gauge must have 12V. I see you are checking that. Good.

The next test is a continuity test of the sender wire I mentioned. A continuity test is to determine if a wire has a continuous connection from one place to another. From one end of the wire to the other. This is to detect a broken wire somewhere inside a long harness, or the wrong wire or any other miswire. To do this you disconnect each end (at the gauge and at the sender) and see if a current will pass all the way from one end to the other. This way you know that the signal is getting from the sender to the gauge. This is done using the continuity test mode on a multimeter or just use the ohm test mode. You must confirm this wire by itself. If there is 12V at gauge and if this wire has continuity......bad gauge.
When you said "continuity across the gauge", I needed to be sure you meant the continuity test I described which is not "across the gauge". The finite detail here is for anyone down the road who finds this post. We are here to help you get this solved one step at a time. I enjoy helping someone figure out a problem. I learn much from it. I learn if my suggestions are valid and in the correct order. Keep us "posted".

Because multimeter test wires are short, you may need to add a jumper wire onto one of the multimeter test leads to reach all the way to the sender end of the wire. Don't disturb the sender wire. Leave it in it's routed position so as to test the situation as it exists.

"If I disconnect the alternator wire with truck running the needle should move yes?" I don't know the answer to that question but it is not the way to determine if amp gauge/charging system is working, as Jerry says.

Lotta words here. Sorry. Words are cheap, miscommunication cost time, money, damage and false test readings.

Got it. I will try this over the next few days.

Is there a way to check my spare temp gauge on my bench?

Sure, use the battery under the hood or take battery to the bench. Hook negative battery test lead to gauge sender terminal and tap positive battery test lead on gauge 12V terminal to see it go to hot...or hook up pos and tap neg. If you remember, I corrected myself and said the gauge case is not grounded. I am not sure, but safer not to ground case.
Use an inline fuse on positive battery test lead.. Use whatever size fuse is used on truck for the gauge.

I use my battery charger for testing, but it is the old school style 10A. Not variable amp/trickle/automatic.

Ok - Tested the spare gauge on the bench and to my surprise the needle jumps with excitement. Happy to know I have a spare gauge when/if I determine the installed gauge is jacked up.
Speaking of the installed temp gauge - I did notice the needle does in fact move when I turn key to on position. It goes in the cold direction and buries there. I was not in the garage to check the gauge but did turn the key to check some other stuff. Did not check continuity yet as describe above. That is still on the list. But, what have I learned by observing the needle to go to the full cold side? Engine was not running and was cold. Do I have the terminal connection at the gauge reversed?

Because the gauge "failed" a test. Seemingly this points to a bad gauge. So you have to get to the gauge.

1. Disconnect battery and pull cluster (disconnect speedo and connectors.)
2. Take to bench, take out gauge and test or leave it in if possible.
3. Check if gauge is wired properly. Don't reinstall cluster until all is well with temp gauge. Also it's possible you will want to test other cluster functions...... other gauges, turn sig lamp, high beam lamp, etc. You can run all the gauges and lights with cluster plugged in, not installed (or installed with two screws), speedo not attached.

Sounds like the terminals on the gauge are backwards (reversed). It shouldn't move any direction when the switch is turned on and it is cold. It should start moving as the engine warms up, the gauge should go up.

As Hotrod Lincoln said, the same wire that supplies the fuel gauge with battery voltage also feed voltage to the temp gauge.

I would look to see if the gauge is even hooked up, or perhaps only one wire hooked up. The new cluster should have the terminals marked which is for the temp sender (green wire) and which is from the ignition switch for battery voltage.

I recently had to navigate through someone else work and they did not hook up all the wires (new wiring kit) and had to sort through what they had and didn't have to get both the temp and fuel gauge working.

Doesn't a "balancing coil" gauge need to have the case grounded to complete some of the circuits? I believe one coil has a constant current flow to ground, and the other coil has a signal with the sensor providing a variable-resistance path to ground that causes the needle to move. A gas gauge works that way, and I believe the electrical temp gauges have similar wiring.

Link- - - - -copy and paste:

https://images.search.yahoo.com/search/images?p=balancing+coil+gauge&fr=yfp-t&imgurl=http%3A%2F%2Flh6.ggpht.com%2F_Ii1ukGkfijY%2FSqopRPyzMvI%2FAAAAAAAAC5Y%2FXflKtuCee-U%2Fclip_image004_thumb.jpg%3Fimgmax%3D800#id=0&iurl=http%3A%2F%2Flh6.ggpht.com%2F_Ii1ukGkfijY%2FSqopRPyzMvI%2FAAAAAAAAC5Y%2FXflKtuCee-U%2Fclip_image004_thumb.jpg%3Fimgmax%3D800&action=click

Jerry

I was in the barn today and had an extra hand so I ran some more tests. When I turn key to on, needle goes cold and stays there.
1. Continuity - Did not get continuity at the terminals of the sender wire. Did not want to believe since new harnesses throughout.
2. Ran an independent wire from sender to gauge. Connected other terminal of gauge to 12v. Engine had been warmed since I was showing off to my friends. Needle came off cold and was reading about what it should have.
Next move is to check continuity of the sender wire to the firewall and then to the panel. Not crazy about chasing wiring of new harness.
I assume the ground is good and the continuity is the telltale?

Are we sure the needle should go hot when key turned to start? I did not read that in my owners manual.
Thanks for the continued advice.

Good news, I think? Can't you trace by color? Don't remember anyone saying gauge should go to hot with key on. Just during a grounding test.
Just to be sure about wording....continuity is between the ends of a wire when it's disconnected at both ends. There are no terminals involved. You are just testing a wire. (you said "terminals of the sender wire"). Sorry to be so ridiculous sounding, in my former life the wrong meaning can cause all manner of chaos and going down the wrong paths during troubleshooting. Conveying by posting is a tricky business sometimes.

The sender wire could go thru a connector or two, I guess, on it's way. In other words, not a continuous wire. If that is the case, test each continuous wire that makes up the path. Start at the sender end (disconnected) and follow wire to the connector. Unplug the connector and see if there is continuity to the connector pin that wire goes to. If you get continuity, leave connector apart, check continuity between the mating pin and to next connector, if any, or to the disconnected end at gauge. Loss of continuity can be a miswire or connector not making contact. Just don't include any components in the test except connectors. When you find loss continuity, you will discover the problem.

Yes I believe you have proven that the gauge is good, the sender is good, but the sender wire is not. Just don't get fooled, like using a different 12V wire on that last test. Hope you used the wire that was part of the harness.
Very good work do far. This is what it takes, unfortunately. It's what is making you an expert. It's really rewarding to find and fix a problem. It's why a mechanic is worth his/her fee. No OBD on these trucks. Isolation, testing, elimination and deduction.

Try tracing circuits on a B-52- - - - -there was over 100 miles on wire on one of those things back in the 1970's, and I'll bet the newer ones have a few circuits we couldn't have imagined back then!
Jerry

That's what I'm talking about Jerry. There can be no errors in certain fields. That's why Aircraft have triple redundancy. Three different harnesses for the same thing. Run in three different places on the aircraft. That can be the case for wire cables, hydraulic tubing, instruments and so forth. No matter how electronic the cockpit instruments got, (LCD Displays and etc,) the chief pilot or military office wanted a glass bubble for inclinometer/turn and bank, a barometric altimeter, pitot tube, magnetic compass and a flash light. For when the "lights went out" sort to speak. No electricity needed for those. The last plane I worked on had all that.

Yep- - - -that's how we made it home a few times with gaping holes in the plane where all that sophisticated stuff used to be! One B-52 I remember made it back to Okinawa with a 4-foot hole in the right wing when a turbine-driven hydraulic pump blew up inflight.
Jerry

The 777 has a propeller driven pump that deploys out the side of the plane in an emergency. Forward movement spins the prop to get pressure. Separate system than the main hydraulics.

Thanks for reinforcement. I M tracking. Yes i did use the harness wire for 12v. Happy to have figured an easy method for that. Unlike b52 i think i may have 2 to 3 connectors to run thru.
Love working under the dash. It is great fun.

Got to it today. Continuity lost in the cluster harness. Had an extra harness on hand so i swapped it out. Frustrating working under the dash but got it done. Works.

WOW! Anytime you figure out something that hidden, it's a good day. Well done. My offer still stands to help fix the turn sig/column/missing parts. If I get a few pics, I believe I can help solve that. At present, you are reaching out to the wrong person. You can start a new post or contact per my previous PM. We will get it done.

With salt on the road and as cold as it has been I have not visited with the 62. Maybe late this week I will get to that one. Happy to be working a few nuisance things off my 66 list.

Roger