Fuel gauge.

[okiemark]

I can't figure out this fuel gauge. One time when you turn on the switch it will go right where it needs to be, next time it goes all the way to the right past full. Works about half the time and about half the time it doesn't

[bmorgil]

Mark, usually full scale is a bad ground. Try jumping the ground on the gauge.

[LarrBeard]

Mark, didn't you have temperature gauge problems as well? I think you replaced the original temp gauge with a mechanical gauge - but I could be getting my Jeeps confused.

If you are having gauge issues, I still suspect the instrument voltage regulator as the culprit. If the regulator quits regulating and just applies 12-volts to the gauges, the fuel gauge will go fullscale.

[okiemark]

Yes, the temp gauge wouldn't move at all so I went with a mechanical gauge. I think it was just a bad gauge. I have checked everything I can think of on the fuel gauge to check. It worked yesterday when I filled the tank. I watched the gauge move up like it should. Later I went to move it and it went out of sight over full. If if comes down to it, how would I know what gauge to get to just have a separate gauge and forget about the one in the cluster? I might try taking the wire that jumps from the fuel gauge to the temp gauge off and see if the temp gauge is messing with the fuel gauge.

[okiemark]

OK, another question. Is the current regulator in the gauge internally. The gauge guy sent me a troubleshooting manual and when I started testing it indicated problems with the current regulator. I'm wondering if changing out the gauge would fix that.

[gmwillys]

Sounds like the ground is intermittently making contact. That would explain the part time issue. I'll have to look at the gage I pulled out of the wagon. It should be the same as yours. If I remember correctly mine wouldn't read water temp either, but would read fuel level.

[okiemark]

I don't mind fixing stuff, but I hate it when you buy new and it doesn't work. That chaps my a*s*s.

[bmorgil]

I am thinking you are chasing a bad ground.

[LarrBeard]

OK, another question. Is the current regulator in the gauge internally. The gauge guy sent me a troubleshooting manual and when I started testing it indicated problems with the current regulator. I'm wondering if changing out the gauge would fix that.

Arrrghhh....

Troubleshooting over the internet is a pain in the tasssk.

Your CJ 5 is a 1957 if I trace things back properly. It would have been an early 12-volt vehicle so at least originally the regulator would have been an external regulator that looked like a little sardine can. It was an obvious add-on to the cluster. It had a wire connected back to the rest of the vehicle (switched 12-volts from the ignition switch), either a little short wire or a tab going over to the gauges (oil, fuel and temp) and a ground terminal that was also a mechanical mounting.

I've been guessing "regulator" - BMorgil is guessing "ground" and I think we may both be right. (Don't tell our wives, it's not my month to have a day to be right.)

Take a good look at the ground tab or screw or whatever that mounts the regulator sardine can to the cluster, and check the cluster ground to the frame. No ground, no regulation - just 12-volts out and a pinned gauge.

This isn't as complicated as mounting a wheat or corn head on the combine - its just trying to do it remotely.

Now, "Is the current regulator in the gauge internally?"

Not on the early CJ5's as far as I can tell. The early ones had a "two terminal" fuel gauge; one terminal went back to the regulator and one went to the sender in the tank. Later ones up in the 60's some time went to a three terminal fuel gauge with an internal regulator; one terminal was the switched 12-volts which went to an internal regulator, one terminal went to the sender in the tank and the third terminal was 6-volts or so that drove the other gauges.

Since your gauge works properly some of the time, you have the two terminal/three terminal thing figured out.

Look for a rusty/corroded/loose ground, like the lights on the grain trucks...

[okiemark]

Well, first of all I can eliminate rust. Everything is brand new. Body, wiring, gauges, everything. It has a 12 volt alternator with internal regulator. I have a ground cable that goes from engine to frame. I also have a ground that goes from the back of the speedometer cluster to the body. Everywhere I check I get a good ground. I will look to see if I can find that "sardine can" in the old dash. The diagram shows a "12 volt" wire directly from the battery to the back of the fuel gauge and that jumps over to the temp gauge. This thing does read about 14 volts when it is running, maybe that is an issue.

[LarrBeard]

Well, first of all I can eliminate rust. Everything is brand new. Body, wiring, gauges, everything. It has a 12 volt alternator with internal regulator. I have a ground cable that goes from engine to frame. I also have a ground that goes from the back of the speedometer cluster to the body. Everywhere I check I get a good ground. I will look to see if I can find that "sardine can" in the old dash. The diagram shows a "12 volt" wire directly from the battery to the back of the fuel gauge and that jumps over to the temp gauge. This thing does read about 14 volts when it is running, maybe that is an issue.

Here is a sketch of some things I found this morning.

If you can't read it, drop me a PM with your email address and I can attach a much better picture than I can post here.

14 volts is great - a sign of a healthy system charging the battery.

In my diagram, there is a 12 volt wire to the fuel gauge, but a separate wire jumpered over to the Temp gauge (6-volts or so to Temp) - the so-called third terminal.

None of us had considered a pinched wire to the fuel sender yet. I have punched wires with metal screws, clamped them between metal edges and made just about every uh-oh in the book.

[5JeepsAz]

It's the float inside the tank. It's either gradually less floaty, or sticking. You owe me a Cherry Coke next time for the consulting fee. This is true because I don't understand any of the above explanations, so I dumbed it down to a mechanical problem. Lol. Good luck, and yes, mine does same thing!

[okiemark]

Everything is new. New tank. New sender. New wires. I checked to make sure the sender was grounded and that the tank was grounded. BUT! Here is something I did find. I went back and looked at the old dash panel and what did I find attached to the back of the speedometer? A little box that looks sorta like a relay. Two terminals. One wire went to the fuel gauge and jumped over to the temp gauge. When I get time I am going to get that little bugger off of there and hook a jumper from the battery to one terminal and check the voltage at the other side. This has to be the current regulator they are talking about, but so far I can't find one you can buy. You can tell this is originally factory wired in, but the wiring diagram in the owner's manual shows it but not in detail.

[okiemark]

Yep, that diagram represents just the way the box was wired in on the back of the old speedometer. Would it be too much to ask for that old relic to work?

[gmwillys]

You'd be surprised to find out it works flawlessly. I have voltage regulators for 6 volts that looked like they were eaten then crapped off a cliff, but they still work just fine.

[bmorgil]

If it does not work it's not a big deal. 12volt to 6volt inverters are cheap nowadays. A solid state one would work real well.

https://www.amazon.com/12-volt-6-dc-converter/s?k=12+volt+to+6+volt+dc+converter

[okiemark]

It actually looks pretty good. Under the dash has kept it protected.

[LarrBeard]

Yep, that diagram represents just the way the box was wired in on the back of the old speedometer. Would it be too much to ask for that old relic to work?

Well, we finally did get something right!

Your new cluster appears to have the three terminal fuel gauge (right?). If it does, that takes the voltage regulator out of the picture unless we are really chasing a strange failure. The new gauge has its own regulator built into it.

If you want to just look at the old regulator for kicks, 12-volts to the input, ground the can and look at the voltage on the output. If you have a little digital meter, the display might jump all over the place because you are seeing a set of contacts opening and closing. An old analog meter might bounce around.

In one of your posts you said:

"The diagram shows a "12 volt" wire directly from the battery to the back of the fuel gauge and that jumps over to the temp gauge."

If you look at the printed diagram I sent, notice that the wire from the ignition loops around that jumper to the temp gauge, it isn't connected to the temp gauge directly - just through the jumper.

Make sure that you have it connected per the printed OMIX diagram.

Here is a suggestion:

Like most intermittent problems, you can't fix it when it's not broken. Get a piece of wire that you can connect to the fuel sender terminal of the gauge and bring it out to where you can get to it and measure the voltage from the fuel sender terminal to ground. Depending on how much gas in in the tank, it should run from about 1 volt to about 6. When the gauge goes full scale, I'll bet that voltage drops to almost zero - a short somewhere between the sender terminal on the gauge and the sender terminal on the tank. With installing a new harness, that's more likely than a bad gauge.

[okiemark]

Well, I asked a question about the regulator to KW and he wrote back and said the regulator is internal to the gauge cluster, so I am trying to find out if all I need is a new fuel gauge.

[okiemark]

I'll check that out. Also I used some of that flex tubing that you put around wires all the way from the gauge to the sender, but I will check for a possible short.

[LarrBeard]

I'll check that out. Also I used some of that flex tubing that you put around wires all the way from the gauge to the sender, but I will check for a possible short.

The flex tubing is a good idea. the tubing protects from pinches and too tight turns around sharp corners. It sounds like you've done all the right things.

[okiemark]

I rewired everything from scratch and put the protection tubing around everything. I found a kit in a bag at Atwoods that had all different sizes of that stuff.

[5JeepsAz]

Yeah. That's great. Just dandy. I'm. So... Does the thing happen to work? Lol

[okiemark]

I think they are sending me a new gauge.

[okiemark]

KW sent me some new gauges. Got time to put them in today and great news! The fuel gauge is working right! I am not using the temp gauge but put the new one in anyway just for the heck of it. The funny thing is when you looked at both gauges, nothing looked visibly different. My reputation was also at stake here because I was convinced the gauge was the problem and I was sure glad when that pin went up about 3/4 way and stopped.

[5JeepsAz]

Glad it's working. Oh yeah, you were right. All along. But I'm still convinced it was a mechanical problem! lol

[bmorgil]

It is a big relief when your repair actually works! But it's the fact you knew you had it all along, right?

[okiemark]

Of course.