Fuel gauge or sender.

[okiemark]

Well, I'm getting this thing wired up. Turned the switch on to test and the fuel gauge goes to full with no fuel in the tank. I pulled it, nothing looked out of order. Clipped a jumper from the flange to ground and same thing. Moved the float up and gauge moves further up. Checked my order and the information says 6 or 12 volt. What am I missing?

[LarrBeard]

A. I don't remember what you are restoring. CJ-??. Has it been converted to 12-volt from 6 volt?

Let me do some poking, but it sounds like a gauge/sender mismatch.

[okiemark]

Yes, CJ5, but I bought a new speedometer cluster and fuel sender. It says good for 6 or 12 volts.

[LarrBeard]

There is a lot of information out there about fuel sender resistance; some of it is suspect – as in where the writer says there are X-amount of ohms flowing through the meter. But, here is a quick check to see if you have a sender problem.

Sender resistance:

Float all the way up – tank full to overflow 0 to 6 ohms

Float at normal full 7 to 9 ohms

Three-quarters About 15 ohms

Half About 22 ohms

One-quarter About 30 ohms

Low About 45 ohms

Float full down (absolutely empty) Greater than 70 ohms

Now the kicker is that when many car manufacturers changed over to 12-volts from the older 6-volt systems, they really did not change the instruments and senders. Instead they installed an instrument voltage reducer to run the oil, temperature and fuel gauges from a nominal 6-volt source (usually a little less than 7-volts).

This made the gauges work in 6-volt or 12-volt vehicles; but in 12-volt vehicles only if there was a voltage reducer installed.

I suspect that you have a vehicle converted to 12-volts - or built as 12-volts. CJ-5's were originally 6-volt vehicles, so they fit this description perfectly. The gauges and senders say “6 or 12 volts”, but what they don’t say is “*Requires instrument voltage reducer for 12-volt systems”. This sounds like your problem!

You can see from the picture that the voltage reducer was often an "add-on".

There are a number of products out there that claim to be “12 to 6 volt voltage reducers”. They range from just a simple series resistor – which is an unregulated band-aid approach, to a variety of bi-metal reducers that may or may not match the electrical load of your Jeep.

Here is what appears to be a good electronic replacement for the bi-metal reducers and it will do a good job for your three gauges. None of the good ones are cheap – but I do not recommend any of the simple series resistor reducers.

https://www.vintageautogarage.com/12V-6V-VREG-Oil-Gas-Temp-Gauge-Voltage-Reducer-p/vreg06703.htm

A quick way to check this out is to get a six-volt battery (even one of the big lantern batteries will do) and run the gauges from the six-volt battery. If they act normal, we've found the issue.

Since all of the gauges run from the same source, you will have oil and temperature gauges that read strangely once you get the critter running.

[okiemark]

I will look into this. Thanks. I might call Kaiser Willys too since that is where I got all this stuff.

[gmwillys]

A pretty reliable reducer is the ballast resisters that Chrysler points ignition systems. GMs used them as well, up to the HEI distributors. They are fairly cheap as well.

[LarrBeard]

A pretty reliable reducer is the ballast resisters that Chrysler points ignition systems. GMs used them as well, up to the HEI distributors. They are fairly cheap as well.

The voltage drop across a ballast resistor will vary as the current drawn by the load changes. In the case of just the gas gauge, the current through the gauge and sender will vary from about an amp (full tank) to a tenth of an amp (empty tank). There will be similar, but probably not as drastic changes in the oil and temperature gauge loads. AS the load changes, the voltage to the gauges will change.

The ballast resistor works well in its intended application because the load current is set only by the coil resistance and is constant (plus/minus very small variations due to temperature).

[gmwillys]

I've been wrong before, it won't be the last.

[okiemark]

Then I checked the temp gauge, and it doesn't seem to work at all. I put the jumper on the sender and to ground and the gauge doesn't move, so I'm going to have to give a call to KW.

[LarrBeard]

Then I checked the temp gauge, and it doesn't seem to work at all. I put the jumper on the sender and to ground and the gauge doesn't move, so I'm going to have to give a call to KW.

Here is more than you want to know about that gauge.

https://www.thecj2apage.com/forums/water-temp-gauges_topic3337.html

It appears to have originally been a mechanical instead of electrical gauge. You get a gas or fluid in the capillary tube hot, it expands and moves the needle.

If you have an electrical gauge with two terminals and an electrical sensor on the engine, someone has done some more "new and improving" on the Jeep - kind of like the oil line and brass plug.

Do you have power to one terminal of the gauge?

[okiemark]

Yes, I bought a new speedometer and gauge cluster. I wired it like it showed. There is a jumper that goes from the fuel gauge to the temp gauge that supplies 12 volts. It already had an electronic sender. I can run a jumper from the sender side to ground and the gauge doesn't move, but then if I tap on it some, it will move up to about 1/4 so it seems to be stuck. Unhook the jumper and tap and it will go back to low. Another thing that happened was that I was hooking up my lights and trying to get that all straightened out and noticed when I had the lights on the fuel gauge would work better. The battery was a little low and it was getting under 12 volts with the lights on, so I'm thinking the problem with the fuel gauge is too much voltage.

[bmorgil]

This is getting deep. It's a good thing LarrBeard and gmwillys are on board. The "switching this on affects that", reminds me of hunting for bad grounds.

[LarrBeard]

Yes, I bought a new speedometer and gauge cluster. I wired it like it showed. There is a jumper that goes from the fuel gauge to the temp gauge that supplies 12 volts. It already had an electronic sender. I can run a jumper from the sender side to ground and the gauge doesn't move, but then if I tap on it some, it will move up to about 1/4 so it seems to be stuck. Unhook the jumper and tap and it will go back to low. Another thing that happened was that I was hooking up my lights and trying to get that all straightened out and noticed when I had the lights on the fuel gauge would work better. The battery was a little low and it was getting under 12 volts with the lights on, so I'm thinking the problem with the fuel gauge is too much voltage.

I'm working with too many Jeeps here. I had you with a CJ-2A yesterday. Your temp gauge is indeed an electrical gauge.

Ask Mike if your cluster needs a voltage reducer to work on a 12-volt system. I am still suspicious of "works on 6 and 12-volt systems"

[Old Marine]

Can I piggyback on this thread?
1962 M38A1 24V. When purchased, ignition on, fuel tank pegged full independent of gas level. Found fuel sender broken (float off of sender shaft). Replaced with Kaiser Willys 24V fuel sender. Also checked wire from gauge to sender (continuity good and about 8V with ignition on). With ignition on, gauge reads 1/8th to 1/4th with known full tank. Replaced gauge with Kaiser Willys 24V gauge... same results. I'm at a loss. Help!

[LarrBeard]

"..Can I piggyback on this thread?.."

Sure, we're not really picky, just tag along here.

It's a bit of a pain, but the surest way to isolate this problem is to pull the sender out of the tank. Use an ohmmeter and measure the resistance from the "hot" contact to the case. At full it should measure pretty close to zero ohms and at empty up around 70 ohms. That verifies that the sender works.

Hook the sender to the gauge and ground the case. Swing the float up and down. The gauge should run from E to F. You've verified that electrically everything is working.

If everythihg works up here, you have an issue with float travel and I ccan't remember to save my neck which way to go. Bend the float arm down and put the sender in a full tank. If it reads higher, you're going the right way, keep bending until a full tank reads full. If that was the wrong way, bend it back the other way and see what happens. It's not an exact science and sometimes you have to decide if you want E to be really dead empty, or Full to be running over full.

[okiemark]

Also make sure all grounds are good.

[Old Marine]

Also make sure all grounds are good.

Sounds like a plan. I ran the ohmmeter with the sender still in the tank and got 37.9. Hate to take out the sender yet again but then it isn't doing me any good mounted so why not.