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That would be a good way to test a gauge still in the dash. I have a used one coming so I will rig up a test platform similar so that I can test it before putting the cluster back in the dash.

Just curious, how exact are the resistors? If you measure a 15.7 do you actually get 15.7?
Don't get hung up on having perfectly exact things. Remember the factory gauge cost maybe a buck or two to make and were never meant to be super accurate. Throw in the cost and loosness of the sender and things can vary a decent amout. This is why I suggest getting a decent meter to check things. If everything is cheap like the gauge,meter, high tolerance resistors, and so on, readings can vary greatly BUT the better the parts and test equipment, the better the results should be.

I don't know how long ago it was but there was a member here on the site that was just fighting his fuel gauge system and I offered for him to come over to my house and I set up a table on the deck with a car battery, my meter, some test jumpers, some resistors, a known good fuel gauge, and I showed him test connections and we did this and that and he finally grasped how things worked. He said he was just not understanding how things worked but then once he saw the tests in action and with conversation of questions and answers being talked about he said that was the ticket to understanding things. It's sorta like learning to ride a bike.

On a 0-30 ohm fuel gauge like yours if I had an exact 30 ohm resistor, a gauge that was exactly calibrated to have it read exactly full with that exact 30 ohm resistance in place, then all would be good but then I'm unsure as to how it might read if let's say the voltage was low like at 10V and then what it might read if the voltage was at 15 volts. It might be close and that's going to be acceptable for a thing like a fuel gauge. I don;t think splitting hairs with exact stuff needs to be applied to this setup. If I do though do a test and things are really wrong, then there is an issue that would need to be corrected.

Just so you know, here is a shot of my meter measuring resistance through one test lead, through some test jumper wires, then back into the meter through the other test lead. You would think it would be 0 ohms but it was not. Wire and connections have inherent resistance.

DSC07264.JPG


0.2 ohms is not a lot but might be depending on how precise you want things.

Here is a setup on the deck when I was doing some fusible link testing. I had to add a battery charger due to shorting out a fusible link and this would draw down the reserve power left in the battery.

2016-7-17 Fusible Link Tests (25).JPG


Just be careful that you don't let the smoke out of any wiring or parts due to wrong connections or short curcuits.

Jim
 

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Winch, regarding your question on resistor accuracy, it's really not important for our application if they're off by even a factor of say 10% (15.7 Ohms meter reading might be a 17 Ohm or even 14 Ohm colour code).
What we're looking for in Jim's suggested test is variation of the gauge indicator but, since you asked, they're manufacturing tolerances are usually +/-10% and or +/-20%. This is indicated by a particular colour band.
Having said that, when Custom Jim mentions colour bands, manufacturers wouldn't identify a 0.7 Ohm value . Instead you would see colour bands indicating either a 14, 15 or 16 Ohm resistor. Likely why he measures them before use so he knows what he's dealing with or when accuracy is necessary. One or 2 Ohms is not going to change an outcome on any car circuitry.

If you're really interested in the colour codes and how to read them, here's a reference page that might be helpful.

 

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Discussion Starter #43
This is interesting. I rigged up a bench test device. I don't have resistors yet but when I do they will go between the alligator clips. Of course I was not getting any movement when I first hooked up my old gauge. Then I decided to see what kind of voltage I would see at various points inside the gauge. While touching the probe to one of components the needle swung over to the right which is what I would expect since the sender wire circuit is open. Then I touched it to the ground and the needle swung almost to empty, maybe 1/8 tank. That is how the gauge was acting when I bought the car. I ran out of gas with 1/8 tank showing and it only got up to 3/4 when I filled it. Anyway what ever I did probing around inside it caused it to start working again. I can't wait to see how it works with resistors and then how the used one I just bought tests out.

If you're wondering about my test device, the board it is
Bench test device front.JPG
Bench test device back.JPG
built on is PVC board.
 

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Discussion Starter #44
I went ahead and hooked up the gauge temporarily to the power and sending unit wire in the car. It now reads FULL. Ohmmeter reads 33 ohms on the sending wire. The manufacturer says that sending unit is 0 - 35 ohms so I guess it is working OK now. Still only goes to 1/8 tank when grounded out. If I want to use this gauge can I slightly bend the needle to EMPTY when grounded out?
 

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I went ahead and hooked up the gauge temporarily to the power and sending unit wire in the car. It now reads FULL. Ohmmeter reads 33 ohms on the sending wire. The manufacturer says that sending unit is 0 - 35 ohms so I guess it is working OK now. Still only goes to 1/8 tank when grounded out. If I want to use this gauge can I slightly bend the needle to EMPTY when grounded out?
If you bend the needle down to read empty, then what will happen when the gauge reads full ?, The answere to me would be the needle now will not be at the full mark but below it if you power things back up with your 33 ohms on the sending wire.

I'm wondering could the shunt resistor have an issue ?. I don't know what the value should be but is it's off either due to a wrong resistance and/or wear and tear on the gauge to where now thing are not working together.

I know you have a limited supply of resistors as the one I suggested to get to test things, is maybe one could try in parallel additional resistances (resistors) across the original shunt to get it to vary and then get things reading right.

I do wonder how the gauge comes apart besides the pictures you have already posted and how easily different shunt resistor values could be tried.

The gauges shunt DOES have an effect as to how well the gauge does read. This is why I have learned that additional tests need to be done with resistors. I just have not wrapped my head around what different shunt values then affect the actual gauge readings but maybe think about it and come up with some answers of your own now that you have the gauge out and if comfortable, could do some more testing and diagnostics.

Jim.
 

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Discussion Starter #46
I don't even know what a shunt resistor is much less how to test using various ones??

As for bending the needle I suspect it would bring it down below FULL at 30+ ohms but between the two I would rather have it accurate near EMPTY than FULL if that makes sense.

I'm not going to do anything drastic until I get the used one that's coming and test it out. If it works better I'll use it and maybe play with the original ongoing just for grins.

One good thing this has done is get me back into working on the old 62 again. I've been restoring it off and on for maybe 6 years and haven't touched if for the past 2. I've had the interior at a shop to be redone for 2 years now. I am also working on a console with gauges from a 68 to put in it. So maybe I'll get back on that project as well.
 

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This is the shunt on your gauge. It is a wire wrapped round cylinder on a white insulator with crimped on end tabs that are then riveted to the housing through insulated holes.

1962 Nova Fuel Gauge (2b) Electrical Connections and Shunt.jpg

If you want to stop figuring out what is going on with the gauge, then bend the needle arm. It's your car and you are free to do whatever with it.

Jim
 

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Hey Winch....just looking at the picture in Jim's last post...check the clearance between the 2 lug terminals and the shunt resistors' wire coil. From this (bad) angle, it looks like the one on the left in the pic is very close to touching and might have even disturbed the coil winding. You can see they are 'adjustable' under their respective nuts.
Just to be sure.
 

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Discussion Starter #49
I'll check it out. I didn't think were adjustable. The posts are set and the connectors have little tangs that make it so it stays in place. I might get a little movement out of it though.

I might test it by removing the connectors and using alligator clips to connect directly to the posts.
 

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Discussion Starter #51
Just got a new (used) gauge and it checks out like I would expect. Hooked it up on my tester with the sender wire circuit open and it immediately swung to the far right well past FULL. Then grounded it and it swung to well below EMPTY. Then I hooked it up to the sender wire going to the tank and it dropped from the far right just a little to just above the FULL. I'm going to wait to install it in the dash until I get the resistors I ordered just to see how it tests out with those.

Whoohoo
 

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Discussion Starter #53
Got my resisters in the mail today. New gauge tested out perfectly I guess. Now to put it back in.

New gauge tested  grounded out.JPG New gauge tested at 7.5 ohms.JPG New gauge tested at 15 ohms.JPG New gauge tested at 22 ohms.JPG New gauge tested at 30 ohms.JPG New gauge tested  with circuit open.JPG
 
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