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Old 07-30-2009, 09:16 PM   #1
kittenb
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Default Testing the Fuel Gauge

Hi all, I need help
I have a 76 Scout II. I bought it at the first of the year and the fuel gauge has never worked. Before going thru dropping the tank and testing the sender I was wondering if there was a way to test the fuel gauge itself. I have grown tired of knocking on the tank to listen for an echo.

Thanks!
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Old 07-30-2009, 09:50 PM   #2
Eric VanBuren
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Default Re: Testing the Fuel Gauge

The biggest cause of failure of the fuel gauge to work is the cheap stamped steel nuts connecting the gauge to the circuit board.

Disconnect the battery and pull the fuel/amp cluster from the dash, don't disconnect the plug just pull it out far enough to tighten the nuts, you will usually find them finger tight. Re-attach to the dash and see if it works.

If that doesn't fix it the best way to test is to go to your local radio shack and get a pack of 10 and 33 ohm resistors.

There is a disconnect at the rt rear of the truck for the wire leading to the sender. Disconnect that and connect a 10 ohm resistor to the harness side wire and a good clean ground. With that connected the gauge should read at the "f" +/- a needle width. Connect a 33 and 4 10 ohm resistors in series and connect those to the wire and ground that should make the gauge read "e" +/- a needle width. That will test the gauge and all the wiring.

If it fails the test there, you can test at the back of the gauge. The terminal on the rt side of the gauge is the one that goes to the sender. You need to be very careful testing there, because the wires that connect to the ammeter are always hot if the battery is connected.

While you are in there I recommend replacing the stamped steel nuts with brass ones. It is one of the first things I do when I get another IH. They are 10-32. I never disconnect the plug from the circuit board as the pins on the circuit board are somewhat fragile and can come out of the board when you disconnect the plug. Those pins being loose can also be a cause of the gauge not working.
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Old 07-31-2009, 06:11 AM   #3
kittenb
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Default Re: Testing the Fuel Gauge

Thanks! We did take the plug out last night before I posted I did see one was loose.
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Old 07-31-2009, 06:34 AM   #4
Scoutboy74
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Default Re: Testing the Fuel Gauge

It's o.k. Sometimes you need to d/c the plug for better access to the gauge guts. You just need to be very careful and sometimes even then you can loosen one or more of the pins. This was just a poor design, but hey...it's late 60's tech at it's best. You can bolster the stability of the pins with some solder around the base of each loose pin. Just make sure that the solder you apply around a pin does not create a bridge contact between any other pins.
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Old 07-31-2009, 07:29 AM   #5
kittenb
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Default Re: Testing the Fuel Gauge

Quote:
Originally Posted by scoutboy74 View Post
it's o.k. Sometimes you need to d/c the plug for better access to the gauge guts. You just need to be very careful and sometimes even then you can loosen one or more of the pins. This was just a poor design, but hey...it's late 60's tech at it's best. You can bolster the stability of the pins with some solder around the base of each loose pin. Just make sure that the solder you apply around a pin does not create a bridge contact between any other pins.
Ok thanks. We were going to try to solder the loose one and see if that was the cause. Another thing I noticed. When we unpligged the gauge, the plug didnt have metal rings in all the holes that it plugged into. Would this make it lose contact & not work ?
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Old 07-31-2009, 07:30 AM   #6
kittenb
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Default Re: Testing the Fuel Gauge

I forgot to mention that we just had to clean up the amp gauge due to no power. Boy does she start like a dram now
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Old 07-31-2009, 08:23 AM   #7
Eric VanBuren
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Default Re: Testing the Fuel Gauge

On the fuel/amp gauge there aren't that many circuits that are actually used so no not every position in the connector will have pins and wires. You'll also notice that there is one female pin w/o a wire, this is to index it so you can only plug it in one way.

If a pin is damaged soldering is a good idea but that can be difficult some times. The other option for some of the connections is to use a ring terminal under the stud and splice that to it's respective wire, by-passing the pins and connector. It is also important to note to only disconnect one nut on a gauge at a time to prevent it from moving around in the housing. The only insulation is a piece of cardboard, move the gauge out of center and the stud can short out on the housing.
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Old 06-12-2010, 06:01 PM   #8
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Default Re: Testing the Fuel Gauge

I realize this is an old thread but felt the need to add a "me too"...

Eric's advise was spot-on. The fuel gauge on my 1980 traveler was not working. Tightening the nuts on the back of the gauge fixed the problem. I'll replace the stamped nuts as suggested, but that will have to wait until tomorrow.

You guys are great!
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Old 11-10-2016, 07:51 PM   #9
J Scout 2
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Default Re: Testing the Fuel Gauge

I know this is a old thread but looking for a little Scout wisdom! I can't get my fuel gauge to work. I checked the nuts on the back side, but noticed that there was nothing connected behind the fuel gauge. Just the battery/amp? Is this correct wiring? New to the IH world! Thanks for the help!
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Old 11-10-2016, 07:59 PM   #10
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Default Re: Testing the Fuel Gauge

And this the opposite side attached to the amp. This is on a 75 scout2.
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Old 11-11-2016, 07:34 AM   #11
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Default Re: Testing the Fuel Gauge

That's the typical configuration. The way the oil temp and fuel gauges work is via a regulated voltage signal that is transmitted via a constant voltage regulator (cvr). The cvr is a tiny device that is attached to the printed circuit board (pcb) on the rear of the oil/temp gauge cluster. The signal from the cvr is passed along in daisy chain fashion among the three gauges I mentioned above. The ammeter gauge is not tied to the cvr. It serves as a bridge between the battery and the alternator, so it functions completely independent from the other gauges. Question for you. How are your other two gauges (oil/temp) behaving? If they are also not working, there's a good chance that your cvr has failed. If your fuel is the only one of the three not working, that means your cvr is still good and you'll need to do some more sleuthing to figure out what's going on. It could be an issue with the sender in your fuel tank, or with the wiring in between the gauge and the tank sender, or even the gauge itself...or in a worse case scenario...all the above! That would be unusual. Usually it is just one of the issues listed, but determining which one will take some patient and methodical checking on your part. One thing I've noticed from your pics is that there is quite a bit of corrosion present on the backside of those gauges. Corrosion and free flow of electrons don't go together. Also, whenever you handle that amm/fuel cluster, you need to be damn careful that you don't short those ammeter terminal connections to ground. The ammeter gauge is in direct connection with the battery, so its live and hot if the battery is connected. Best thing for safety is to unhook your battery whenever you plan on handling that cluster. As far as cleaning the corrosion and tarnish on the copper traces of the pcb's, you don't want to use anything abrasive. A pencil eraser works well for shining that copper back up. Also, the square, plastic gang connector on those clusters attaches to a group of very delicate pins that are swaged into the pcb. If you remove that gang connector, just be very careful and work slowly. There's not much holding those pins in place and if they get loosened, that will affect gauge performance also.
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Mongo - '71 1210 Std Cab 2WD - 345/TF727/RA17 D60 4.10 Trac-lok - "Mongo love candy! Duh, huh, huh!"
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Old 11-11-2016, 08:07 AM   #12
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Default Re: Testing the Fuel Gauge

Quote:
Originally Posted by scoutboy74 View Post
question for you. How are your other two gauges (oil/temp) behaving? If they are also not working, there's a good chance that your cvr has failed. If your fuel is the only one of the three not working, that means your cvr is still good and you'll need to do some more sleuthing to figure out what's going on. It could be an issue with the sender in your fuel tank, or with the wiring in between the gauge and the tank sender, or even the gauge itself...or in a worse case scenario...all the above! That would be unusual.
I very much appreciate the response. I was told it might the sender by the guy I bought the Scout from a month ago or so. I also followed the advice when working on electronics disconnect the battery. So I will look into a fuel sender and see what happens.
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Old 04-12-2018, 06:53 AM   #13
meisterj
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Default Re: Testing the Fuel Gauge

Reviving this informative thread with a gauge failure question. Scout II, cleaned the tank, redid all the lines, new sending unit all about 6 months ago. Gauge has worked since I got the Scout 1.5 years ago. Last night I put in half a tank of gas and on the way home all of a sudden the needle started to drop slowly. It went from 1/2 to E over about 1 to 1.5 minutes. Does this mode of failure indicate a possible cause. I am guessing that a loss of electrical continuity would cause an immediate movement to E not a gradual movement to E. Any thoughts before I start to take things apart?
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Old 04-12-2018, 07:20 AM   #14
Scoutboy74
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Default Re: Testing the Fuel Gauge

Assuming your TEMP and OIL gauges are still functional, about the only piece that can be immediately ruled out is the CVR. Everything from the gauge to the in-tank sender is a potential culprit.
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Favorite hobby...Driving Salma Hayek in my Scout

Coal Trickle - '99 Dodge Ram 2500 Q-Cab SWB 4x4 - 5.9L 24V CTD/NV4500
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