Fuel Gauge acting like an Ammeter

[athawk11]

As some of you know, I'm finishing up a CJ3A for my wife.� I got all the electrical done this weekend.� I drained the battery down pretty well while working out some lighting/grounding issues.� I was happy to see the ammeter start to function correctly after polarizing the generator/regulator.� When accelerating, the ammeter needle jumped to the positive which indicates the system is recharging the battery.� Excellent.� When I turned on my headlights, and only at an idle, the ammeter dropped to the negative.� Good.� Just what I hoped to see.

But then I noticed the oddest thing.� The fuel gauge was mimicking the ammeter.� For every movement on the ammeter needle, the fuel gauge needle did exactly the same thing.� I'm mystified.

Any ideas on what I did?� Or what may be going on?

This is a 12v reproduction ammeter and fuel gauge.� Pretty sure I hooked up the Walck's harness correctly.� Everything else works perfectly.

Hawk� �

[scoutpilot]

I�m sure you added the ground for the sender plate. Did you add a ground for the gauge itself? �New Repro� may require it.

[athawk11]

Hi Scout,

I did add an additional ground to the sending unit plate.  (Seen below)  The newer fuel gauges have 3 contact posts.  One for power (+), one for the sending unit (in the center marked 'S') and one for the ground (-).  There is no wire included for this 'ground' in the Walck's harness...and no reference to it in their instructions, but I added a ground wire on my green Willys (which works fine), so I added the same wire to this one. 

[1955CJ-5]

Does the gas gauge work normally other than having the needle move one way or the other along with the ammeter?  The fuel gauge on my MG moves one way or the other depending on whether or not the fuel pump is running...just reacting to the voltage fluctuations..

Maybe when your battery is completely charged the fuel gauge will settle down...

[athawk11]

That's a good question Randy.  I don't know yet.  I haven't run it long enough to fully charge the battery.  There is about a 1/4 tank of fuel, but the fuel gauge doesn't drop much below 1/2 tank, but climbs to about 3/4 full as I accelerate.   Pretty much like the ammeter.

The fuel gauge is the type that you can fine tune with a small screw driver.  I haven't done this yet.  I guess I'll fill the tank,  try to eliminate the extra ground wire, and maybe disconnect and reconnect the feed wires to see if this 'shocks' it into reading accurately.  This is strange. 

[1955CJ-5]

I have no doubt that you will figure it out.

Let us know when you do!

[1955CJ-5]

I keep thinking about this...Thinking out loud now...

Normally power goes to the gauge and then to the sender and then to ground...

Now you have power to the gauge, then power to the sender, and then ground directly back to the gauge....

Maybe grounding the gauge to the frame, and then the sender to the frame would break the loop?

At least now the faster you go the further you can go!

" but climbs to about 3/4 full as I accelerate."

[athawk11]

At least now the faster you go the further you can go!

Wouldn't it be great if that were reality?  

I diddled around with it a bit last night.  I removed the extra ground wire that I added to the gauge's (-) post.  There was no change.  I imagine the gauge is getting a ground through the mounting bracket.  I also disconnected and reconnected the power wire.  No change.  I adjusted the gauge so the needle would show the right amount of fuel.  The reading still increases when accelerating.

I'm wondering if the voltage regulator needs to be adjusted/turned down a bit.  I'm not sure how to do this. 

My next moves will be the charge the battery, and fill the tank all the way.  Not sure that this stuff will make any difference.

[1955CJ-5]

I think there is a long description of how to test and adjust the voltage regulator in the manual...

I tried it once and gave up almost immediately..

There is a shop here that is supposed to be able to adjust regulators, but they wanted the generator too..

I found it easier and cheaper to buy a new regulator..

I suppose the sending unit is 12 volt or does that even matter?

[Ryan_M]

This probably doesn't help but the last repro fuel gauge I bought ended up going in the trash can. No amount of "fiddling" got it to work right. It wasn't doubling as an ammeter like yours is but would only pin dead full or dead empty. No amount of grounding combinations would fix this.

I'm sure there was something else I could have done -- some step I was missing -- but I ended up finding a good used one and installed that instead. No issues.

[Oilleaker1]

My "Ford" kit car used a Motorcraft 12 volt alternator. The Smiths instruments I used were originals. They were "over ridden" by the mass voltage that they were not used to having. LOL, English  I had to install a resister to drop the voltage feed down so the gauges weren't pegged when I reved up the engine. Maybe this same idea would help your gauges. Oilly

[aboyandhisdog]

Far be it from me to offer advice on this Tim, but it sounds to me like you're getting some kind of a cross feed maybe at the IGN switch?  When I went from an ammeter to a volt meter, I remember having an issue getting wired up correctly as they don't connect the same.  Now I know you have always used ammeters and no doubt it is wired right, so I wonder if you might change the terminal on the switch for the fuel sender/gauge and see what happens.   

BTW, the voltage (6 or 12) makes no difference as far as the sender and gauge are concerned, but the ohms does have be the same on both.  I believe 33-240 ohms is the most common, but if both aren't the same, you're going to have problems.

[Tumbleweed]

Tim,

I remember having an issue with my new gauge as well. On the back of my gauge there were 3 connections. I purchased the gauge from KW and when I called them to see if they could help with my problem they told me to run a ground wire to the body from the back of the gauge. I believe I connected the center post to ground. Do you have 3 connection posts on your fuel gauge? If so this may be the culprit.

[athawk11]

Hi Tom,
The gauge is marked 12v. The sender and gauge came from Walck's and appear to be identical to the set I purchased from them for the OD Willys.  I believe I have the gauge connected the the 'ignition' on the key switch.   I do have the 'accessories' post on the key switch.  I'll try connecting it there and see what happens.

Tumble,
The fuel gauge sounds like the same version I got from Walck's.  It has 3 posts.  (+), (-), (S)  I connected the power feed to (+).  I connected the sender to (S), and finally I grounded the (-) to the tub.  I did remove the ground to see if there was a change, but the gauge acted the same way with no ground connected.  I removed the Sender feed from (S) and moved it to (-) but got no reading at the gauge.

I suspect I'll get this figured out eventually.  I do appreciate the feedback.  It does help.

Tim

[Gunslinger]

Just a thought here, you can pick up some pretty decent gauges at a reasonable price from most auto parts stores.  Replace the gauge you are struggling with just to see if this will eliminate the problem.  If the new gauge works right you will know if its a gage problem, if it goes wonky as well you will know its a sender/ wiring problem.  Might help you focus the problem solving.