fuel gauge wiring

Guys, this is a simple question.....i think.

I have seen wiring diagrams for the later cj fuel gauge. The one with 3 terminals. But I can't find a diagram for the older 2 terminal gauges. Orgionally, there was a jumper wire from the fuel to the temp gauge. I have that in place. But what goes on the other terminal? 12V? Wire from the sender?

From the wiring diagrams (3 terminal gauge) it appears wires should go rom batt to gauge terminal to sender to ground. The other terminal is only a jumper wire. Does not seem right.

The wiring diagram I saw today on a newer cj showed 2 wires on the fuel sender. One came from one of the fuel gauge terminals and the other to ground. Is this correct?

I thought the sender had 3 wires to it.

I also need to incoporate a 6v gauge. I was going to try using a 12v sender, droping it to 6v then on it's way to the gauge. Any thoughts?

But for now, I just need to know what attaches to the two terminals on the fuel gauge.

 

Sparky, I really don't know. Like I said, the wiring diagram I've seen appear to somehow to be wired into a 12V supply. It looked like this on two diagrams I looked at today. One for a 72 to 75 cj and one for a 76+.

But then again, the two diagrams I looked at were for 3 terminal gauges, not two terminals.

I can't find this out on the internet. All I find is for the newer gauges.

For such a simple thing, this really sucks. Does the 12V supply go to the sender, then to the gauge, then to ground? This is how I thought it worked. And if that is the way ti works, I should be able to get the gauge to work.

Any help would be appreciated. THis can't be as difficult as I'm making it out to be.

 

Just a hunch but I think that the two terminal fuel gauges are for 6 volt systems.

the third terminal is output from an internal voltage regulator which feeds the jumper to the temp guage. the regulator drops the 12v input to 5-7volts for both of the gauges to work on.

if indeed it is a 6 volt gauge, the jumper would go on the same terminal as the 6v supply, carrying the 6v to the temp gauge. then the other terminal would have the sender wire on it.

 

I just ordered a NOS speedometer cluster from Peter Debella to replace my current non-functioning unit. What is the proper method of grounding the the regulator to avoid the output of the regulator from rising to the battery voltage and smoking the new guages? Since this is a new unit with the internal grounding already be done or will just properly grounding the cluster also ground the regulator?

 

As Howard stated above, if your fuel gauge is two terminal it's probably 6V and will need a regulator which will be a small metal can with two studs and a tab attached to the bottom of the can. This tab is used for mounting and ground. It must be grounded. If you have the cluster that has three studs on the fuel gauge (12V), then it has the built in regulator. However the speedo housing will have to be grounded as the internal regulator gets it's ground from the speedo housing.

 

The cluster that I currently have does have the three terminals. Hopefully the new one will also. One of the terminals appears to go to the sender, one to the ignition and the third is the metal strap that leads to the temperature gage.

What's the best method to make certain that the case is properly grounded. Currently the only ground that i can see is the physical connection when it is bolted to the dash panel.

 

Yes that is the normal connection. Your main concern is that the dash panel has a good ground to the tub and that the tub is grounded to the negative terminal of the battery. This is usually accomplished by a ground strap from the engine to the frame, then another strap from the frame to the tub. A sure-fire way would be a separate wire (ground) from cluster mounting bolt directly to an engine bolt.

 

Great advice,

Thanks

 

Well, The new speedo showed up yesterday. I got it installed last night. I ended up running a ground from the speedo case directly to the battery just to ensure a good ground.

When I turn the ignition switch on, the guage climbs from Empty to Full. I have the sender unit grounded to the frame.

Any thoughts? After researching the post here it sounds like the sending unit might be bad.

 

If you remove the sender wire (screw in the middle) the fuel gauge should drop to "E". If this is the case, then you know the wire from sender to gauge is good. What you don't know at this point, is the float arm stuck in the up position. After removing the sender from the tank, with sender wire on center screw, and the frame ground wire connected to the sender housing, you can manually move the float arm up and down and watch your gauge move.

 

I'll give that a try. Sure not looking forward to droping that tank. But I have a feeling I'll need to.

 

Well, I checked the wire from the sender to the guage and everything checks out fine. It looks like i'll need to lower the tank and take a look at the sender.

Will I damage the fuel guage by disconnecting the sending wire and driving the Jeep? I was going to drop the tank when it warms up a bit. I'd love to use the Jeep but since its a brand new guage, I don't want to risk burning it out.

Thanks

 

No damage, since the sender is unhooked the circuit is incomplete and no juice goes through the gauge.

 

Your temp gauge should be working normal correct? Only the fuel should show empty all the time with sender wire disconnected and taped over eyelet to keep from accidental grounding. The internal regulator in the fuel gauge will still be drawing current as the bi-metal strip (regulator) has it's own circuit to ground so the temp gauge will continue to work.

 

Thanks Walt. Will it damage the Fuel Guage?

 

No, as alex211 said-- there are two components inside the fuel gauge. 1 is the regulator and 2 is the needle gauge movement. The needle movement circuit has to have a resistance on it (sender) before it can complete the circuit. So you will not have current flow thru this part of the gauge as long as the sender wire is not grounded. So no damage will be done if you run it this way for ever. HTH
Walt

 

Finally received a new sending unit to test. I hooked the center post to the sender location on the guage and connected the ground to a ground. The guage appears to be off by 1/2 tank. Empty shows I have a 1/2 tank on the guage.

Will this resistance change when the unit is actually in the tank with fuel? is there a way to manually calibrate either the guage or the sending unit to read correctly?

The unit reads 75 Ohms empty, 28 Ohms at 1/2 tank and about 8 Ohms when full.

Thanks

 

The sender being in the fuel will not make any changes to your sender resistance. The readings (resistance) you show, have you in the ball park for proper operation. Be it known that these readings are for the Stewart Warner and Jeep fuel gauges. After-market types will usually have their own senders specific to their gauge. What manuf. gauge are you using (fuel/temp combo)?