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Advice Needed On Replacing Fuel Gauge
Topic Started: Jul 27 2009, 12:48 PM (722 Views)
dstrickler
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Stricks
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I am considering replacing my fuel gauge. I believe it works, but it's for a 6-volt system, and my 3B has been converted to 12-volt. I've seen 12-volt gauges on eBay for about $25.

It looks like replacing it is just a few bolts, and some small wiring hookups. While not very handy with a wrench, I understand wiring, and overall it seems like an easy task.

Have any of you replaced one of these, and if so, is there something I'm missing? Is it easy, or a royal pain?

Instrumentation panel

Thanks,
Dave
1954 CJ-3B
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Daryl
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3/8 nutdriver and 5 minutes of your time.
Lotsa Jeeps, and a few extra parts
In Bonney Lake, Washington
Always willing to look at a Jeep for you BEFORE you buy it to check it out.
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1954cj3b
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piece of cake :) Posted Image
3b'ers do it on all 4's
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Larry (TX)
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ds,

Like Daryl says, it isn't hard at all; that is unless you have very large hands and/or a bad back (as the position you may have to take can be strenuous).

If you really want to make it even easier (and this allows you to see what you're doing since you've obviously never done it before) and it takes only a few more minutes to do, follow these simple steps:

1. disconnect your positive battery cable (it's real easy to get stars and stripes started under a jeep dash if you're unfamiliar with where positive leads are attached).

2. reach up behind the speedometer and unscrew the ring nut securing the drive cable, then pull out the cable housing and drive, lay aside; there are two 3/8" nuts that secure the odometer to the dash by way of a (square) horseshoe shaped bracket; remove the two nuts and bracket, then the odometer will slip out of it's mounting hole.

3. now you'll be able to see the back side of the fuel gauge and it removes in the same manner that the odometer does, except that it has wiring ( a positive and a negative wire) attached to the two mounting posts. The horseshoe bracket will have insulators built in; the fuel gauge is polarity sensitive, so take care to replace the lead wires back the same way you removed them.

As a suggestion, I'd stick with a good quality, name brand gauge which you should be able to purchase at any local auto parts store and save your shipping cost on an e-Bay sale. Also if you're unaware, you can purchase the gauge with a built in lamp.

Hope this adds additional assistance to your question.

Larry S.
Larry Steed
Pearland, Texas
'53 Willys CJ3B
'52 Willys M38
'86 Chevy M1009 CUCV (K5 4x4 Military Blazer)
M100 1/4 ton jeep trailer
M416 1/4 ton jeep trailer (2 ea.)
M101 CDN 1/4 ton jeep trailer
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donk
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Did your sending unit change also?
1953 CJ3B/Hurricane F-134/
Bantam TC-3 trailer

Hampden,MA
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cjric
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Cant you just add a resistor in line before the gauge?
Mine had a resistor w/ the original 6v gauge/sending unit. Only problem with mine is that whoever wired it put the resistor in between the gauge and sending unit, not before the gauge. So now I've got to replace it.
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dstrickler
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Stricks
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Thanks for the heads-up that this is pretty simple. I'll attempt it in a few weeks when I have a free afternoon and the part.

Larry S: Excellent instructions (ever thought about writing a HowTo on 3Bs? I'd buy it!).

Regarding using a resistor in series with the fuel gauge, that's not going to give you an accurate reading as the fuel runs low (or high, depending on how it's wired). On the other hand, it may be useful enough to know "is there some gas in the tank or am I SOL..". I debated on doing that myself, but decided against it due to inaccurate readings, although I will say 15 minutes with a soldering gun and a 10 cent resistor seemed like a good fix!

Dave
1954 CJ-3B
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dstrickler
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Stricks
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To give some closure to this post, I replaced the fuel gauge last weekend to with limited results. First off, for an amateur like me, it was pretty simple. Getting the old gauge out and the new one back in wasn't hard although I had my brother-in-law to the reaching up behind the dash. There are only a few bolts, and it's not bad.

Dealing with the electrical took us some head scratching. The old gauge had only two electrical posts, and the new one has three. Turns out that the labels on the new posts are "+", "S", and "-". The "+" goes to the wire that comes off of the ignition switch. It's the hot lead - pretty obvious. The "-" goes to the ground on the cassis - pretty obvious. The "S" through us for a loop, but we found on the CJ3B site that the "S" was the lead off of the gas tank's rheostat. "S" stands for "Sending Unit" - the rheostat.

Once this was hooked up, we fueled the jeep up all the way, and adjusted the rheostat on the back of the gauge itself so it would read "Full".

While this all works electrically, it looks like the rheostat on the fuel tank isn't working, as I can drive the jeep for miles and the gauge never moves. So, time to replace that part too. Since the jeep was converted to a 12 volt (from 6 volt), I think it may just be the original rheostat feeding a bad signal.

More news as it happens...
Dave
1954 CJ-3B
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jyotin
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The + terminal is for the 12 volts coming in.

The - terminal is for the ground

The S is the wire to the sender.

I'd disconnect the ground lead from the battery before starting this job.

Also DO NOT try to test the system until it is completely installed. It is tempting..... but don't. See below for why.

Make sure that you have a good connection to ground on the - side of the gauge.

What happens here is that the 12 volts goes through the gauge to ground via the - terminal on the gauge and the sender unit (S terminal) changes the total resistance of the circuit so as to deflect the gauge.

The system is set up so that 99.999999999% of the current goes through the meter, and .000000001% of the current goes through the sender (S terminal). This is because the sender is inside the gas tank and no one wants to create a spark in a gas tank.

If the gauge is not grounded (- terminal) and voltage is applied, then the only path to ground is through the sender and the sender in the tank will fry in a heartbeat.

Actually a heartbeat is too long -- my experience is that it occurs instantly-- well not quite instantly either.

But if one really cared to calculate how long it would take to fry the sender, since electricity travels at the speed of light --- compute how long it would take for light to travel around 30 inches at 186,000 miles per second.

good luck - this isn't a difficult repair...

Since you will be into the sending unit anyway, you could also run a good ground wire from the tank to ground. Chances are it is grounded anyway through the fuel line plumbing, but having a solid connection is always better.
It's just my luck that something good is going to happen to me today.
54 - 3B - down on the farm
67 - cj6 - former state of Alabama vehicle
?? - cj5 T98a - made from spare parts - Ford tractor blue
?? - cj5 T98a - made from spare parts - Jeep green
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