Gas Gauge Problems

[Norm's Coupe]

......

[Merle Coggins]

Norm,

If you have an open the gauge wouldn't move regardless of the sender position, and if it has a short it should peg the gauge and again the sender wouldn't have any effect on it. Are you sure the gauge is OK? Did you try checking the wire continuity with an ohm meter?

[Normspeed]

Well Norm, if it's at all like my P24, it's a fairly simple job to add new wires from the dash to the tank. Need to get underneath the car though.

I need to get after the body and headlight harnesses in mine too they're crumbly. I did the engine compartment and OD when I swapped motors but procrastinating on the rest of the wiring.

[47heaven]

After beating my head against the wall with the first gas gauge, I had one of the members on here offer to fix it for me. Not just the gauge, but the sending unit, as well. I sent it back to him and he repaired both of them and said they worked when he tested them. To make a long story short, I got them back and hooked them up according to how he told me, but still couldn't get it to register correctly. I know he repaired them and that they were working for him, but just couldn't get them to work for me. I tried to troubleshoot with the book, but still without any positive results. I recently purchased an NOS gas gauge on Ebay, and since I just converted to 12 volt, I bought 12-6v voltage reducer for it. I connected the reducer between the ignition and the gauge. I made a new wiring harness from the gauge to the sending unit (+ to +, - to -) and grounded the sending unit to what I feel was a good ground...the bolt for the thing the trunk latches to. As a result, when I turn on the ignition, the needle shoots past the full mark and stays. Usually, it would take a few seconds, but this one just moves immediately. Does the voltage reducer have to be grounded, too? I know ziltch about elecronics.

[Plymouthy Adams]

the guage is marked for battery and then you terminal ! and terminal 2 the wires to 1 and 2 go to the terminals on the tank unit..the tank is grounded and the sender unit can be grounded extra for know ground to the body of the sender but never to one of the terminals. The guage cares not if it is positve or negative ground nor if 12 or 6 volts as the guage is heater element with built in voltage regulator in the gauge..the twin coils pull the guage in both directions as the 0-32 ohms are split to ground on the wiper...as the wiper moves the 32 ohms are linear..1 would be 32 and 2 would be 0..as it moves to the other end, and say 1 changes to 25 then 2 will the 7...this balance and the 5 volt regulator dampens the movement against any slosh and keeps the needle rock solid...it also take a few cycles of the built in regulator to steady out the needle and read the tank level accurately.

[Plymouthy Adams]

There-in lies the problem..you have to understand how it works to get it to work...nothing more needs be said...

[Plymouthy Adams]

Whatever..I'm out of it...

[Plymouthy Adams]

I said I was out of it..but this will cinch it...it is funny Norm how you can go round and round about this and that and relate all non car related incidents in your verbage but god forbid someone take a minute and explain something so the guy and back up and regroup...excuse the hell out of me....!!!!!!!!!!

Ed..guess I can kiss one of my Christmas gifts good bye with that one....

I don't apologize for the truth..just for the manner in which I had to put it across...

[FMSPEED49]

You might try running a jump ground from the bumper to the sending unit, not the terminal, just the outter ring , and see if it will work, mine did all kinds of funny things, figured out the gas tank wasn't grounding well with the new rubber covers on the straps, i solved this problem by running a ground wire the edge of the sending unit, to make sure it stayed grounded and my gauge straighten right up.

also btw , i figured out if your cork floats are bad, you can replace them with the plastic ones for a riding lawn mower, but you need two of em to make it float right.

if that doesn't work, try running a seperate wire from the sending unit, around the side and touch it to the terminal on the gauge, this will tell you if it is the wire, and if it needs to be replaced.

[Don St Peter]

I just went thru the same thing as described below. 2 to 1 it's an insifficient grounding problem in the end.

Don

[T.Tom Meshingear]

A lot to read but good info - especially the troubleshooting section

Tom

[47heaven]

Okay...before I do any tests, I wanted to show what happens to my guage in two different stages. The first diagram shows how everything is connected when the guage reads past FULL and stays there until the ignition is turned off.

Below is the same diagram, but with the wires switched at the sending unit. When I did this, I got an EMPTY reading and the needle twitched a couple times, but never advanced.

Again, I am using a 12v to 6v voltage reducer that is wired between the ignition lead and the guage. The reducer is grounded by a wire from it to a bolt on the dash/cowl vent lever support. Also, the gas tank is full.

When I connected the ignition lead to the guage without the voltage reducer, and wired as shown in diagram 1, the needle did the same thing and shot past FULL. I didn't try it with the switched wires. As far as I can tell, the guage is not fried, yet, because it didn't smoke during these tests. I wanted to post this and have you look it over to see if maybe this is enough info to possibly see what may be wrong before perfoming the other tests.

Note: I made a mistake when I initialized "ignition" on the voltage reducer diagram and put "ing" instead of "ign."

[Plymouthy Adams]

You are using + and - for terminals 1 and 2 and that is okay as long as 1 goes to one and 2 goes to two..the second chart is incorect....the first wiring should be correct..the black box you have below the tanks sending unit..what does that represent...?? This should be the sending unit going to ground....as the tank is full in this confition, the guage will read full as you indicate in your test. Using the trouble shooting chart above you can test each leg of the resistor by grounding or open by just lifting the wire off the terminal, through the wiper on the reisitor...as posted in picture by Tom T.

Do not depend on the tank itself being a good ground connection..you can run an alternate ground wire to the frame of the car..please keep in mind here also that the lower part of the sending unit, the bulge that the reistor fits into is the ground point mechanically for the wiper..the sender has a gasket between it and the tank and internally between the bulge and the top cap where the terminals are..you can take a short piece of wire and place it between the sender and the tank with the gasket under the wirre and bolt it down..this wire can now go to your car body and ground ensuring a good connection at this point..seriously sounds like ground is your problem.

In regard to your reducer..if this is one of the type that bolt in and not electronic or bi-metal style as built into your guage..the load will not be enough to reduce you voltage..they work well on larger load device but WILL still surge on first power then fall back. What voltage are you reading on the guage side of the reducer with the ign switch on? Can you post a pic of your reducer...?

Again, the guage will work without the reducer as the guage itself has a built in 5 volt bi-metal regualtor.

The ground is the one most common problen to these guages not working. As indicated in earlier post and pictures above..the wiper, arm that the float connects to, is the only link to ground you should have on the sender.

[Guest mikeys toy]

Let me jump on this subject;

I just went to 12v neg. ground and need to hook up the gas guage

I have an old voltage reducer with one input and 3 outputs marked with different amperages. However, when I run 12.6v through it, I get 11.2 at all three outputs. What ohmage resistor would I need? It's a late '53 Cranbrook with two wires on the back of the guage and one on the sender. Also, which wire would be the stock ign. terminal and the sender on the back of the guage?

thanks in advance....

[Guest mikeys toy]

The back of the gage may be marked if you look closely

NOPE! I looked......one terminial is a bullet, I'm assuming that's for the guage, and the other is a ring terminal, ignition?

[Guest mikeys toy]

I was just going to say you didn't read my first post....

I have a two wire system, but I looked really close and there is nothing marked in the metal or the cardboard.

I can always hook it up and see, but I believe 12v will fry it, so I really need the reducer info first

[47heaven]

You are using + and - for terminals 1 and 2 and that is okay as long as 1 goes to one and 2 goes to two..the second chart is incorect....the first wiring should be correct..the black box you have below the tanks sending unit..what does that represent...?? This should be the sending unit going to ground....as the tank is full in this confition, the guage will read full as you indicate in your test. Using the trouble shooting chart above you can test each leg of the resistor by grounding or open by just lifting the wire off the terminal, through the wiper on the reisitor...as posted in picture by Tom T.

Do not depend on the tank itself being a good ground connection..you can run an alternate ground wire to the frame of the car..please keep in mind here also that the lower part of the sending unit, the bulge that the reistor fits into is the ground point mechanically for the wiper..the sender has a gasket between it and the tank and internally between the bulge and the top cap where the terminals are..you can take a short piece of wire and place it between the sender and the tank with the gasket under the wirre and bolt it down..this wire can now go to your car body and ground ensuring a good connection at this point..seriously sounds like ground is your problem.

In regard to your reducer..if this is one of the type that bolt in and not electronic or bi-metal style as built into your guage..the load will not be enough to reduce you voltage..they work well on larger load device but WILL still surge on first power then fall back. What voltage are you reading on the guage side of the reducer with the ign switch on? Can you post a pic of your reducer...?

Again, the guage will work without the reducer as the guage itself has a built in 5 volt bi-metal regualtor.

The ground is the one most common problen to these guages not working. As indicated in earlier post and pictures above..the wiper, arm that the float connects to, is the only link to ground you should have on the sender.

Yes, I'm using #1 and #2 as A and B. Same on the sending unit. The black box below the unit represents the float. I realized after the fact that I hadn't labeled it. I did have the sending unit grounded when it was 6v. I had connected a wire to one of the screws that is used to screw the unit into the gas tank. I felt that it would be a good source to run the grounding wire off. Then, I ran the wire to the bolt that bolts in the catch for the trunk latch. I'm not sure if this grounded it or not.

The reducer I am using is exactly like this one:

Would something like this work instead, since it's meant for a fuel gauge?

http://cgi.ebay.com/ebaymotors/Fuel-Gas-Gauge-VOLTAGE-REDUCER-12-Volt-to-6V-conversion_W0QQcmdZViewItemQQcategoryZ33674QQihZ008QQitemZ180065250824QQrdZ1QQsspagenameZWDVW

Since I haven't had the new wiring harnes installed, yet, I'm using the old lead wire and connecting that to the end of the reducer that is labeled "bat" and then a wire leading from the other end and connecting to the bottom terminal of the gauge. I then took another wire and connected it to the larger part in the center of the reducer and connected that wire to the center dash support. I sanded the metal before bolting the wire to it to be sure that it had good contact. Does there have to be two places where this fuel guage system is grounded; one for the gauge and one for the sender? Id having it overgrounded not good?

Now, you are saying that the guage will work without a reducer because it has a built in 5 volt bi-metal regualtor (whatever that is). I've been told by so many people that the guage cannot run off of the 12 volts and that a reducer needs to go in between the lead wire and the gauge itself. This is where I'm getting confused. Note that this is not the same guage that I had repaired. This is a NOS gauge that I won off of Ebay, so it hasn't been upgraded.

Also, there's never the chance that the sending unit will spark, will it? If so, that would not be a good scene.

[Plymouthy Adams]

Darin...in reality that particular reducer is not much good for light loads the guage will represent..that is designed for heater motors and such...even at that when first energized it still spikes the voltage and as such the motor can handle that so no big deal. The body of the resistor is just a mount and should be no electrical contact to the car...battery in on one side and load (device) connected to the other...your sending unit should be grounded in the following manner due to age, corrosion and such over all the years...this will provide a solid ground and should remove all doubt..get a small thin piece of copper or brass material..say about 3/8 wide and about maybe about an inch long, approx. .010 inch thick and drill a hole in each end..place the gasket on the tank mounting flange..then one end of the strap..then place the sending unit in so that the main lower body contacts the strap, curve the other end of the strap to contact the upper plate of the sender and attach an aux ground strap here and run to know good clean body ground.

In the schematic above, the picture of the guage at the bottom left says CONTACT..this is the internal switching contacts on the bi-metal that regulates the input to 5 volts..reading under operation explain how it works. This is why they can work on 12 volts..the contacts open and close at a faster rate than on 6 volts..but even on 6 volts they are constantly are opening and closing..that is why the guage moves in small increments when you first turn it on.

If you do not have a good Volt/Ohm meter by now..do yourself a favor and do get one..they are not expensive anymore and are worth thier weight in gold when doing electrical work and trouble shooting..

I will be running mine on 6.2 volts steady regualted DC with a device I built that will handle 12 AMP load..size of a golf ball and toatally adjustable output..can handle a direct short and fold so as to prevent burn out. I would recommend that you find such a device for yourself..and save the other resistor for a wiper motor, heater or such as that. It really is not instrument grade device.

[Merle Coggins]

Let me jump on this subject;

I just went to 12v neg. ground and need to hook up the gas guage

I have an old voltage reducer with one input and 3 outputs marked with different amperages. However, when I run 12.6v through it, I get 11.2 at all three outputs. What ohmage resistor would I need? It's a late '53 Cranbrook with two wires on the back of the guage and one on the sender. Also, which wire would be the stock ign. terminal and the sender on the back of the guage?

thanks in advance....

Is your resistor connected to a load when you measure the voltage? If not you won't see the voltage drop. A basic rule of electricity regarding resistances in a series circuit... The voltage drop across each resistance will equal the total voltage. The voltage drop accross each resistance will be dependant on how much resistance each has. Does that make sense?

Here's a basic diagram to help explain. This is from my Basic Electric course that I have taught to our technicians. Construction equipment is commonly 24V, which is why I used 24V in the diagram.

[Guest mikeys toy]

Hmmmmm.

but wouldn't the higher ohmage (word?) represent a further drop in voltage?

[Merle Coggins]

Higher resistance (larger ohm value) will consume less amperage and more voltage. This can all be calculated with simple math.

The formula is V = I x R (Voltage = Amperage x Resistance) Don't ask why "I" represents Amperage. I used to know, but I can't remember right now.

With a little algebra we can convert the formula to find the missing value.

I = V / R or R = V / I or V = I x R

If you measure the resistance of your gauge and your resistor (voltage reducer) you can determine what the voltage drops will be. (Assuming this is on a converted 12 volt system, you should use 14 volts for your calculations because that should be your charging voltage.)

Add up the resistance values of your gauge and resistor. Now 14 divided by your total resistance will = the amperage draw of the circuit.

Now take your calculated amperage and multiply that number by each resistance value to determine what the voltage drop will be across each resistance.

Example;

Your gauge measures 3 ohms of resistance

Your voltage reducer (resistor) measures 4 ohms

Total resistance = 7 ohms

14 / 7 = 2 amps

2 x 4 = 8 volt drop across the resistor

2 x 3 = 6 volt drop across the gauge

8 volt drop + 6 volt drop = 14 volts (a way to check your math)

Does this help clear it up?

Merle

[Guest mikeys toy]

Ummmmm......durrrr?

*scratches head*

actually it does, but my eyes glazed over as soon as I saw the word 'algebra'

for me, there IS no simple math, but I got it figgerd out

[Plymouthy Adams]

Darin..the solid state device you show appears just to be a zener diode..

This is the picture of the one I put together..

[Chester Brzostowski]

Higher resistance (larger ohm value) will consume less amperage and more voltage. This can all be calculated with simple math.

The formula is V = I x R (Voltage = Amperage x Resistance) Don't ask why "I" represents Amperage. I used to know, but I can't remember right now.

With a little algebra we can convert the formula to find the missing value.

I = V / R or R = V / I or V = I x R

Why I = Amps…

Current is defined as the number of electrons to flow through a point based on a given period of time which is one second..

The most basic unit of charge is a Coulomb. A coulomb is defined as A meter-kilogram-second unit of electrical charge equal to the quantity of charge transferred in one second by a steady current of one ampere. The theory was developed by Charles A. de Coulomb (1736-1806).

The I represents Ions ( Remember the early inventors first explored magnetism and tried to explain it before they actually defined electricity as we understand it today. The acronyms carried forward.

An Ion is defined as an atom, group of atoms, or molecule that has acquired or is regarded as having acquired a net electric charge by gaining electrons in or losing electrons from an initially electrically neutral configuration. Etymology: Greek ion, something that goes, neuter present participle of ienai, to go.

Basically electron movement is measured in Amps which represents movement of electrons from one atom to another. This movement is defined as Ion theory. Thus Amps is denoted as capital I for Ion ( to go )

Chet... Keeper of useless information