The Stovebolt Site Forums The Shop Area The Electrical Bay Fuel gauge not reading.

I need some help. The fuel gauge was not reading when in the dash. I pulled it out and it works on the bench. Used an old sender to check on the bench.Checked the line from the dash to the sender and it’s good. Before putting it back in the dash tested it again because I wanted to eliminate the sender in the gas tank. Worked fine. Installed it back in the dash and it does not work. Looks like it is not get power because when you turn on the key, nothing happens. I have power from the key to the gauge. What am I missing?

Did you change to a 12 volt system? Look up ‘runtz’ accessories!

Ed

He did, at least on the bench.

Yes. 12 V conversion. But using the voltage drop so I can continue to use the original gauge.

Make sure the internal ground on the gauge is clean and making good contact with the case.

Yes, cleaned both gauge and case with emery cloth. Plus the gauge worked testing testing on the bench.

You never explained what happened when you turned on the key.

Does the gauge indicate empty, full or some intermediate value?
How much gas is in the tank?
What happens if you ground the wire at the sending unit?
What happens if you remove the wire at the sending unit?

Here is a procedure I wrote on testing a faulty gas gauge. This goes though testing every component in the system that may help diagnose your issue. Especially read section 6.3

Testing a Gas Gauge on a Stovebolt
Written for a ‘47 thru ‘55 first series, but may work for other years

The steps are as follows:

1. At the sending unit, remove the wire that goes to the gauge. The gauge should go to full. Now touch the wire to a known good ground. (Run a jumper to the battery negative if unsure). The gauge should go to empty. If you pass both of these tests, that tells you that the sending wire and the gauge are OK and the sending unit and/or the ground at the sending unit is the issue. Check sending unit grounds. Clean contact surfaces and/or replace wire and connectors.
2. If your gauge still does not work, remove the sending unit from the tank. Be prepared to buy or fabricate a new gasket, as it’s usually stuck to the tank. First, shake the float to see if it has been leaking. If there is any gas in it, it’s shot and will need to be replaced. We’ll test the sending unit to see if we replace the whole unit or just the float. To test, use a multimeter and set it to the lowest ohms scale (mine was 0-200). Place the positive (red) lead on the terminal that goes to the gauge and the negative (black) lead on the sending unit body making sure you have good contact (sand/scrape if you have to. Now move the float. At empty (float all the way down) it should read 0 Ohms (or close to it). At full (float all the way up, it should read 30 Ohms (or again close to it). If the unit works, you can buy a new plastic float from eBay. Look for one that fits a Jeep, 1955-1983 CJ5, 1955-1975 CJ6, 1976-1986 CJ7, 1981-1986 CJ8

3. Test for 12 volt supply on the gauge (the one from the ignition switch) if you find no voltage, fix/replace the supply wire.

4. Do a continuity test on the sending unit wire to the gauge. If you have an open fix/run a new wire.

5. Run a jumper wire from a known good ground to the back of the gauge cluster to insure the cluster has a good ground to the dash. If you gauge works you’ll need to clean up the area where the cluster touches the dash.

6. Unfortunately the next step is to remove the gauge (Disconnect your negative battery terminal before you start).This requires you to remove (or drop) the gauge cluster which houses the fuel gauge. I was able to lower mine sufficiently in order to remove the gauge. The bezel is crimped in a few spots which holds the assembly together. Using a small screwdriver, carefully pry open the crimps. Once the bezel, glass and inner trim are removed the gauge is visible. To remove the gauge, the adjacent gauges need need be loosened. There are two tabs (visible in the picture) that are behind the adjacent gauges and will prevent you from removing the gauge. Once loosened, you can remove the gas gauge. There are a few things to check. At this point, use the battery (or an external battery such as a motorcycle, tractor, auto, etc) so we eliminate any bad ground issues.

6.1. First let’s check if the gauge functions properly. Connect a jumper from the negative side of the battery to the sending unit terminal (the one with the red warning label). Connect a second jumper from the negative side of the battery to the gauge ground (shown in the picture). Connect a jumper from the positive side of the battery to the power supply terminal. Your gauge should go to empty. If it does not, the gauge is bad.

6.2. If your gauge checks out good, look at the back of the gauge where the gauge ground makes contact with the gauge cluster frame and clean/sand the contact area, insure there is no paint, rust or anything else inhibiting a good ground contact. Reinstall the gauge back into the cluster frame and tighten the nuts. Re-perform the gauge test but use the gauge cluster frame as the gauge ground. If the gauge now test good it’s time to reassemble. Tighten the adjacent gauges to the cluster frame.

6.3. There’s one more thing we need to check before we reassemble. Some of the reproduction gauges are made slightly thicker and the needle gets caught on the inner trim piece inhibiting the needles movement, making the gauge look like it’s not functioning. If you find this condition, a gentle push with your fingers will give you the additional clearance you need to keep it from binding. Mind you I do mean gentle as it moves easily and you don’t want to distort the inner trim piece. Once you have determined the needle moves freely, reassemble the rest of the cluster. The first time I installed the bezel, I used a screwdriver and a small hammer to crimp the bezel to the cluster and I felt it jared the cluster too much. The second time (yes, it took two times to get it right) I was able to use a needle nose pliers to get the crimps in. Protect the chrome from getting marred. Maybe some other “Bolters” have some other ideas on how to crimp the bezel on to the cluster. Now reinstall the cluster and hopefully it works! (Don’t forget to reconnect the negative battery cable)

7. At this point, we have eliminated everything but the sending unit. If your gauge still does not work, remove the sending unit from the tank. Be prepared to buy or fabricate a new gasket (you can’t use Silicone Gasket Maker as the gas will soften it and it will fail), as it’s usually stuck to the tank. First, shake the float to see if it has been leaking. If there is any gas in it, it’s shot and will need to be replaced. We’ll test the sending unit to see if we replace the whole unit or just the float. To test, use a multimeter and set it to the lowest ohms scale (mine was 0-200). Place either lead on the terminal that goes to the gauge and the other lead on the sending unit body. Now move the float. At empty (float all the way down) it should read 0 Ohms (or close to it). At full (float all the way up, it should read 30 Ohms (or again close to it). If the unit works, you can buy a new plastic float from eBay. Look for one that fits a Jeep, 1955-1983 CJ5, 1955-1975 CJ6, 1976-1986 CJ7, 1981-1986 CJ8.


Hopefully, at this point, you issue is solved!

Phil, a great piece of work. I found this with the search engine last week. Printed it out and had it on the work bench with me. It has to be a grounding issue but I won’t be able to get back to this until next Sunday. People like you make this a great site and resource. Cheers!

You can use a voltage reducer, but you don't need one, Darren. Your fuel gauge cares more about amperage than voltage. However, my work has shown if you use the gauge at 12 v it will not register properly at 6v again. The permanent magnet inside the gauge is magnetized more strongly and that alters it forever. If you want an adjustable voltage reducer, just contact me. Same size as the Runtz adapter but much more flexible...allows you to adjust your fuel gauge to show full with a full tank accurately.

Wouldn't adjusting to show empty with an empty tank be more important?

I would think adjusting the gauge to say empty when there's a little gas left in the tank might be practical.

Dean

It seems logical you could adjust it at either empty or full, but I believe adjusting at full is better. There are 2 important variables. Let me try to explain and I'll keep this as much out of the weeds as possible. I have mentioned a few times before the permanent magnet (the hourglass shaped metal piece) in your gauge will gain magnetism by being exposed to 12v. According to a friend who has many years more electronic education than I, that little piece is also going to de-magnetize just sitting there for 60 years, so its condition probably will be different today. But according to him, this loss/gain will not ruin the gauge but will change how it registers and that fundamental change will require the proper voltage/amperage to make it register correctly today. Let me repeat: the gauge will work just fine at both empty and full....as long as it gets the proper amount of juice and the proper resistance to ground (through the fuel sending unit). More to follow. Unless you know the full history of your truck and equally importantly the fuel gauge in it, you don't know what has happened to it along the years. Now, the gauge doesn't care nearly as much about voltage as it does about amperage (even though they are inarguably linked), but higher voltage will increase the emf (electromagnetic field) and it will increase the magnetism of the thin metal hourglass shaped piece. When your tank is empty, your sending unit tells your fuel gauge there is zero resistance to ground. When your tank is full, your sending unit tells your fuel gauge there is 30 ohms resistance to ground. If all is well with your gauge (and by this I mean it is adjusted so that 30 ohms resistance gives you a nice full reading), then you will have a nice empty reading when the resistance is zero. That is the way that gauge is made. If you have an adjustable voltage regulator and a fuel gauge which has some unknown degree of magnetism, you can actually watch as you adjust the output higher from 6v and see just when you hit F.

Inside the fuel gauge you have two coils...and they're different (they're even different colors). See image below. You have a choke coil and you have an operating coil. The choke coil pulls the needle (which is attached to the hourglass shaped metal piece I've mentioned) toward the empty side. The other coil (the operating coil) pulls the needle toward the full side. Electricity enters the choke coil when the ignition switch is turned on. That coil is connected to the operating coil...and the tank sender which provides either ground or resistance to ground, depending on the level of fuel. The other end of the operating coil is connected to ground. Okay, now if you have an empty tank, the electricity ends up going to ground through the sending unit. With all the juice going to ground through the choke coil, that coil is turned magnetic and it pulls the needle to empty. If the tank is full and you have 30 ohms of resistance at the sending unit, then most of the juice runs through the choke coil, into the operating coil and then to ground. This pulls the needle to full. The operating coil has more and smaller gauge wire windings, so it takes less juice to generate enough magnetism to over-ride the choke coil and pull the needle toward full.

So, assuming a good fuel gauge is going to work correctly if it receives the right voltage (which is linked to current...sorry, but basically it is) then adjusting to full (which requires you adjust through 30 ohms or whatever your sending unit provides at full) will set the upper limit. Adjusting only to ground misses this important part. And that is why you need to start with full...you may think your sender is registering 30 ohms at full, but years ago I proved right here not all senders will do this. In fact, I only know of one being sold which will do so predictably. If your sender is giving you 22 ohms or 45 ohms at full and you've adjusted things so that F registers correctly at that resistance, the 0 ohm resistance to ground (Empty) should follow naturally.

Thanks Jon

Thank you for all your responses. I have an update. Removed the sender lead and the gauge goes full. Attached the lead from the gauge to the sending unit, the gauge reads 1/4 tank. So it seems the gauge is working. Now turn the key off. Then turn the key back on and the gauge stays at empty and does not move. I am going to assume this is a sender problem. I am looking for input because the tank is not behind the seat seat any longer but under the bed. Dropping the tank will be a pain. Thanks in advance.

I was just going to post a request for fuel gauge help. Don't want to sabotage your thread Darren.

From other bolters' posts, you might try checking ground. Run ground from sender to frame. Also a ground (new sheet metal screw) from gauge cluster housing to one of the 3 mounting bolts. Good luck.


Now, my question to the forum - did I really BLOW a 2 new fuel gauges?
I replaced the gauge in my 12v 1955e. But I crossed the wires and by all accounts killed it. So...
I installed a 2nd new gauge this week and did this... Please Comment....
After connecting the ground from sender to gauge, I attempted to connect the 12v, BUT, upside down under my dash with my glasses slipping, I put the 12v on the SAME post. Unknowingly, I turned the key to see if the needle moved. Nope. I quickly turned off the key and corrected the wires.
My gauge is stuck at 3/4.
Did I kill number 2?
Any ideas?

Don, thanks for the comments. Yes, the ground to the sender is good from the sender to the frame. Used a little emery cloth to ensure the connection is good. I also added a ground wire from the cluster housing to the frame. I have conductivity from the sender wire at the gauge to the sender ground wire. But I did not pay attention to what the resistance was. Something else I will check today and make sure I have a 0-30 ohm sender. It was supposed to be 0-30 but you never know.

Darren. A few ideas.

* Something interfering with indicator needle (touching glass face etc.).
* The fuel gauge movement is contaminated or worn (sticking).

I have posted this numerous times but will repeat it here again. A couple of years ago I embarked on a fuel sender unit project designed to make the best fuel sender available. I bought units from all over the place, spent hundreds of $$, made scads of images and recorded output from everything from the OEM sender to you name it. I can do that...make one which at empty is 0 ohms and at full is at 30 ohms and will work predictably, but I can't do it for less than $30 each. And that is what the best fuel sender available will cost you. Go to the big auction site and use advanced search to find the seller named "renbusan". He sells a 0 to 30 sender that was designed and made in Taiwan and the fellow who did the work had his mental ducks all in a nice row. Below is a link that should take you there. ALL OF THE SENDERS I BOUGHT FROM THE USUAL SUSPECT VENDORS WERE SUBSTANDARD. Every one of them. One would register 10 ohms at empty and 40 ohms at full. One would register 0 at empty and 22 at full. One was so erratic it was functionally worthless. And the worst one of all (came from a vendor a lot of people seem to love) was really a 0 to 90 ohm unit that had been reduced to a 0 to 30 ohm unit by the person in China dribbling solder on the resistance coil. Take a look at the image below. Horrible sender and an industrial joke. Take a look at the second image below. Half is wound very tightly so that you would get a nice even needle action. Then half is wound so loosely it can not possibly give the proper resistance reading. The third image shows the unit sold by renbusan. What look like little wires are really individual pieces of metal bonded to the nylon carrier. The black arc over to the right is the resistance strip...poured in place and moved where nothing rubs on it. So it will remain undamaged pretty much forever. That is a sending unit worth having.

Here is a link to the renbusan sender: https://www.ebay.com/itm/261122347319?hash=item3ccc1ad137:g:FBgAAOSwpPVgBuwZ&vxp=mtr

The one I was going to make is shown below. All brass and stainless steel (so nothing to rust ever), a stainless ball to wipe over flat resistance wire (Kanthal wire) and a nylon piece for the wire wrap. Works like a charm, but as I mentioned can't be made and shipped for $30.

The needle moves freely.

I believe your gauge is function as it should, In picture one, with no power, (doesn’t mater if the signal wire is connected or not), it should show empty. Picture two with power on, signal wire not connected (0 ohms) it goes to full as it should. Picture three, power on, signal wire connected (10.4 ohms) shows 1/3 tank., again as it should. When you shut off the ignition (power off), it goes to empty. Mine in my ‘52 operates exactly the same.

The only issue I see is the level is off a bit. The level measures 5” on a 10” tank, should be half of a tank and tells me the float needs to be adjusted.

EDIT: since the OP reposted his reply (originally in the wrong thread), my reply is in response to the post, two posts down.

No, with the wire disconnected the load on the wire is infinity ohms, not zero ohms. But you are right that the gauge should read full (at 30 ohms or more).

Update. Although I was sure the sender was the issue a ran a few more checks and I have included pictures to help show the steps I took. The first picture is with the key off and the sender wire connected. Next I removed the sender wire and then turn on the key, and the needle goes to full. Finally I connect the sender wire to the gauge and the gauge goes to about 1/3 of a tank. But then if I turn the key off and then back on, the needle does not return to 1/3 full. Checked the sender wire back to the tank and it is good. Then tested the ohms at the sender and it is reading 10.4 ohms. Checked the fuel level in the tank and it measure 5" in a 10" deep tank. Makes the ohm reading seem a little low, but in the ball park. If I use my old original sender from the tank that sat behind the seat, everything reads correctly. So does this bring me back to the gauge? Of will I need to drop the tank and test again with the new sending unit in hand.

I know that you said the “needle moves freely”, but I would recheck.

Some of the reproduction gauges are made slightly thicker and the needle gets caught on the inner trim piece inhibiting the needles movement, making the gauge look like it’s not functioning. If you find this condition, a gentle push on the inner trim piece with your fingers will give you the additional clearance you need to keep it from binding. Mind you I do mean gentle as it moves easily and you don’t want to distort the inner trim piece. Once you have determined the needle moves freely, reassemble the rest of the cluster.

What happens to the gauge when you ground out the sending wire at the tank with the ignition on?

you are right and I stand corrected!

The needle moves freely. Just tested the gauge in place using my old sending unit. With the unit set to read half a tank, turn the key on and off and it goes empty when off and back to half when the key is on. I am starting to wonder if the new tank was sent to me with the 0-90 ohm sending unit.

Easy to check with your ohmmeter. Best to remove the sending unit from the tank.

If you have 0-90 ohm sender, the obvious answer is you'll show a full tank with 1/3 of a tank of gas and higher...possibly a bit less or more than 1/3 of a tank depending on how poorly your special Chinese made sender was built. You may be correct about receiving the wrong sender. Please see my post and comments about the sender (above). I've discussed this before, but 30 ohms at full is critical for the AD gauge. It was designed for that resistance to ground amount and will work really well when it gets it. Some people here have opined over the years that the gauge wasn't that accurate. Not true. The sender was plenty accurate but the OEM sender was designed to last for about 5 years at the most and most of the aftermarket senders are so inaccurate it is comical. The least accurate (but cheapest to make) senders are the ones using the inside arch shape. The best and most accurate senders are the ones using the flat surface wiping scheme. I've rewound some of the Chinese specials and have made them work well, but you must use flat resistance wire. They'll be accurate and long-lasting that way, but it is much more expensive and must be done by hand.

You can see below. Good luck!

Sender removed from the tank and it reads 0-30 ohms. With the sender out of the tank it measures correctly on the gauge. Made some adjustments to the float travel and reinstalled in the tank. 22 gal tank. Put 12 gal gas in the tank and it is measuring 1/4 full. I’m happy to see movement of the gauge. Thoughts?

Is the float arm long enough for the float to touch the bottom of the tank and the top of the tank?

If not, you'll only get an approximation of fuel volume.

You can bend the arm if necessary or weld an addition to it if it isn't long enough.

Or buy one of those sending units that Jon Goodman recommends that has an adjustable arm for different applications.

It looks like you can adjust the arm to make it longer/shorter. I would try that.

There is a basic geometric formula, but it isn't important to bore you with it this morning. About a year and a half I posted the image below (when I was doing all the fuel gauge work). At some time in the past I posted a chart I made for all kinds of tank depths. I truly wish we had tech tips or some repository in which this stuff could be stored to make it accessible, but that's another discussion, I suppose. Anyhow, there are only two things about the pivot point drop and swing arm length for the behind-the-seat AD tank you need to know: with either the OEM sender or any of the aftermarket senders, the distance from the top of the gas tank to the pivot point will be 5.5". The OEM sender angled backwards, but it didn't change the depth of the pivot point (and this formula...half of it anyhow is simple...the tank is 11" deep so I expect you've already leaped ahead to that conclusion). The length of the arm will be 6.5" long with the OEM sender (because it pivots further back) and 5 7/8" for all others. Unless you're using those figures, your float can't work properly. Good luck. And please say a prayer for the return of usable tech tips.

One other suggestion: Get a piece of cardboard or paper that gives you 11" of length and enough width for the swing. Set your pivot point right at the middle (5.5"). Now without moving the sender, swing the float arm all the way up. Does it look like it will go to the top of the paper? And swing it all the way down, keeping the pivot point at 5.5". Does it look like it will rest near the bottom of the tank? If it doesn't, try to adjust your rod so that it will (think 5 7/8"). If you don't have enough rod, just go buy a common brazing rod and use it.

Jon, great idea! It takes all of the math and guess work out of it. A common piece of printer paper is 8-1/2 x 11 inches, so it is perfect.

My thought on this is that you don’t want empty at the bottom of the tank. Why not give yourself some reserve at the bottom end. Say 1” off the bottom of the tank? And maybe the same at full.

Some of the original tanks and all of the replacement tanks I've seen are actually a bit taller than 11 inches. There is a horizontal baffle piece in place (cut so that fuel will flow through) slightly above the bottom of the tank...maybe an inch or less. I haven't really cut one apart to look since around 1972. Point being when your float hits that baffle piece (which in mine was 11" from the top) you'll THINK you're empty...but you will have enough to keep going for a while. As for leaving room at the top, no...I would not do this unless I planned on having somebody leave the ignition on and use the fuel gauge to judge how much gas was in your tank (maybe you don't want to fill it up?). I'd make certain the float hit the top of the tank when it was full. That way I'd know the tank and gauge were in concert. Just my thoughts, Darren.

When the gauge reads empty, just open the petcock and drain out what's left to see exactly how much you have in reserve.

I did that out of curiosity around 1980. It was around 3/4 of a gallon. I recall thinking it might get me another 10 miles down the road. If I had a tailwind and was heading downhill.

On the gauge, what is supposed to represent Full and Empty?

Is the two dots on either side of "1/2"? Or is it the actual letters, "E" and "F"?

My gauge doesn't quite go all the way to the letter "F" and goes past "E" when the ignition is shut off.