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Old 08-21-2017, 06:24 PM   #1
paintman
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stainless mustang tank, Autometer guage, bad ground?????

Gentlemen! 46 chevy pickup here andI have an issue with my fuel guage. I re-wired my entire truck front to back with an Amerian Autowire kit and everything works except the fuel gauge. I have a 22 gallon stainless mustang tank with a sending unit that came with the tank. I also called Autometer and had them send me what is susposedly the proper ohm/gauge for the sending unit.

When I key the ignition and start the truck all the guages work except for the fuel reading. The fuel guage light works fine, but the needle stays at empty. Originaly I thought my problem was that the tank was not grounded properly because I mounted the tank with foam weatherstripping under the tank to prevent chaffing (I know I was over thingking it). LOL! Any ways I made up a 10 guage ground wire with ring terminals and mounted one end to the tank using an unused mounting hole. The other end of thw wire I ran to ground on the chassis. Unfortunately this did nothing for my problem

I guess my question is.........What the hell could be wrong? Do I not have my tank grounded well enough with a 10 guage wire? Does stainless ground the same as steel?

Or perhaps Autometer sent me the wrong guage and I'm just pissin up a rope?

I really don't want to pull the whole guage panel apart until I have tried all other options. Can I check the guage by disconnecting the wire at the sneding unit and just touching it to ground with the key on? If the guage is working wouldn't the guage read full at that point?
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Old 08-22-2017, 09:21 AM   #2
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Re: stainless mustang tank, Autometer guage, bad ground?????

In answer to your last question, yes, you can test the gauge by removing the sender wire at the tank, but if you ground the wire, the gauge should show empty. With the wire just disconnected, the gauge should show full (or maybe beyond full).

You say you grounded the tank, but did you actually ground the sender?...and are you sure the sender is 0-90 ohm?

Good luck and keep us posted.
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Old 08-22-2017, 04:18 PM   #3
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Re: stainless mustang tank, Autometer guage, bad ground?????

[QUOTE=lsversaw;8022499] You say you grounded the tank, but did you actually ground the sender?...and are you sure the sender is 0-90 ohm?

Now this is going to sound like a dumb question but.......how the hell do you ground the sender? There is only the one spud on the outside of the tank for the wire from the gauge.

Yes I am dead certain the sender is 0-90 ohm I actually pulled the sender and checked it on the ohm meter.

I am however not certain the gauge is correct. even though I had auto meter send it to me for this application. no telling if the guy behind the phone knew what he was talking about. There are no markings on the guage so its impossible to tell.
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Old 08-23-2017, 12:05 AM   #4
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Re: stainless mustang tank, Autometer guage, bad ground?????

Grounding the sender should be just mounting the sender flange to the tank and then grounding the tank.
If the sender wire is grounded the gauge will read empty. If you disconnect the sender wire from the sender and don't touch it to anything the gauge should read past full. Key on of course. There is the possibility that the sender wire is pinched to ground at some point between the tank and the fuse panel or the gauge if it runs directly to the gauge on your truck.
On the 67/72 trucks the sender wire runs to the fuse panel to a terminal labeled FUEL on the panel and from there it goes to the gauge.

There is also the possibility that the fuel gauge is not getting any power to it and it is just reading empty because it will do that if it isn't energized for a long period of time.
Make sure that you have a power wire to the gauge and a sending wire from the gauge and the gauge also has to be grounded to the dash cluster.
You should take an ohms reading between the sender wire and the tank flange looking for somewhere between 0 to 90 ohms and then check between the sending wire and the tank for the same reading/ This will tell you if the sending unit is grounded to the tank.
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Old 08-23-2017, 06:48 AM   #5
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Re: stainless mustang tank, Autometer guage, bad ground?????

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Originally Posted by VetteVet View Post
Grounding the sender should be just mounting the sender flange to the tank and then grounding the tank.
If the sender wire is grounded the gauge will read empty. If you disconnect the sender wire from the sender and don't touch it to anything the gauge should read past full. Key on of course. There is the possibility that the sender wire is pinched to ground at some point between the tank and the fuse panel or the gauge if it runs directly to the gauge on your truck.
On the 67/72 trucks the sender wire runs to the fuse panel to a terminal labeled FUEL on the panel and from there it goes to the gauge.

There is also the possibility that the fuel gauge is not getting any power to it and it is just reading empty because it will do that if it isn't energized for a long period of time.
Make sure that you have a power wire to the gauge and a sending wire from the gauge and the gauge also has to be grounded to the dash cluster.
You should take an ohms reading between the sender wire and the tank flange looking for somewhere between 0 to 90 ohms and then check between the sending wire and the tank for the same reading/ This will tell you if the sending unit is grounded to the tank.
Hey thanks Vette for all the suggestions! I know I have power to the guage because it lights up upon keying. Also I have all my guages grounded at a main terminal (Ron Francis), grounding block. So if all my other guages are working I can only assume my ground is good. I will have to check the sender when I get home tonite.
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Old 08-26-2017, 01:38 PM   #6
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Re: stainless mustang tank, Autometer guage, bad ground?????

Ok an update. Had some time to crawl around inside and out of the truck, here is what i did. I took the sender wire off at the tank and nothing happened at the gauge. Stayed at zero

Then I took a volt meter and checked power at the terminal on the back of the gauge. I have 12V power at the gauge!

Does this mean I have a bad gauge? I can't imagine a brand new guage being faulty.
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Old 08-26-2017, 11:58 PM   #7
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Re: stainless mustang tank, Autometer guage, bad ground?????

Quote:
Originally Posted by paintman View Post
Ok an update. Had some time to crawl around inside and out of the truck, here is what i did. I took the sender wire off at the tank and nothing happened at the gauge. Stayed at zero

Then I took a volt meter and checked power at the terminal on the back of the gauge. I have 12V power at the gauge!

Does this mean I have a bad gauge? I can't imagine a brand new guage being faulty.
You'll get 12 volts at the back of the gauge between the sender terminal and ground even reading through the resistor or the gauge coils.

The gauge staying at empty means that your sending terminal is grounded either at the gauge, between the gauge and the FUEL terminal on the fuse panel, or in the wire from the fuse panel to the sending unit at the fuel tank.

If you pull the sending unit wire off at the fuse panel, what happens. Your gauge should go to Past full, between the 2 o'clock and the 3 o'clock position.

If it does then you should pull the sill plate over the left rocker panel and check the tan wire for chafing of the insulation where it may be touching the cab metal.

If you have a grounding terminal on the gauge, be sure you don't have the tan sending unit wire connected there instead of to the sending terminal.
HEY it can happen.
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Old 08-27-2017, 11:47 AM   #8
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Re: stainless mustang tank, Autometer guage, bad ground?????

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Originally Posted by VetteVet View Post
You'll get 12 volts at the back of the gauge between the sender terminal and ground even reading through the resistor or the gauge coils.

The gauge staying at empty means that your sending terminal is grounded either at the gauge, between the gauge and the FUEL terminal on the fuse panel, or in the wire from the fuse panel to the sending unit at the fuel tank.

If you pull the sending unit wire off at the fuse panel, what happens. Your gauge should go to Past full, between the 2 o'clock and the 3 o'clock position.

If it does then you should pull the sill plate over the left rocker panel and check the tan wire for chafing of the insulation where it may be touching the cab metal.

If you have a grounding terminal on the gauge, be sure you don't have the tan sending unit wire connected there instead of to the sending terminal.
HEY it can happen.
Ok Vette here is some more info...........
Checked the back of my gauge. I have ignition power wire going to termianl marked "I" ignition. Ground going to "G" and sender going to :S: so thats wired properly accourding to the Autometer and American autowire diaghram.

Not sure what you mean by disconnecting sender wire at fuse panel. American Autowires' harness has the sender wire running directly from the guage all the back to terminal on tank. I did disconnect sender wire from back of guage and checked it there. I get 38.5 on the ohm meter, which sounds right as I know I have 9-10 gallons of fuel in the tank.

I also checked the ground terminal on the back of the guage with the ground wire connected. I got a reading of 0.4 from the teriminal to the main grounding block for all the guages. I guess this tells me that I do have a good ground at the gauge.

sure seems to me I have either a brand new guage that does not work, or they sent me the wrong guage for a mustang sending unit. I think maybe the best thing to do (before i pull the guage cluster out of the dash), is get a new guage that I know for sure is 75-10 and jury rig it to the fuel sender wire and see if i get a good reading.
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Old 08-27-2017, 02:35 PM   #9
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Re: stainless mustang tank, Autometer guage, bad ground?????

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Ok Vette here is some more info...........
Checked the back of my gauge. I have ignition power wire going to termianl marked "I" ignition. Ground going to "G" and sender going to :S: so thats wired properly accourding to the Autometer and American autowire diaghram.

Not sure what you mean by disconnecting sender wire at fuse panel. American Autowires' harness has the sender wire running directly from the guage all the back to terminal on tank. I did disconnect sender wire from back of guage and checked it there. I get 38.5 on the ohm meter, which sounds right as I know I have 9-10 gallons of fuel in the tank.

I also checked the ground terminal on the back of the guage with the ground wire connected. I got a reading of 0.4 from the teriminal to the main grounding block for all the guages. I guess this tells me that I do have a good ground at the gauge.

sure seems to me I have either a brand new guage that does not work, or they sent me the wrong guage for a mustang sending unit. I think maybe the best thing to do (before i pull the guage cluster out of the dash), is get a new guage that I know for sure is 75-10 and jury rig it to the fuel sender wire and see if i get a good reading.
On the stock fuse panel there is a terminal marked FUEL that the sender wire from the tank plugs into. It is just a junction for the sending wire to the gauge. It made the assembly line easier for the factory.

Right edge center.

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I forgot to have you measure ohms from the hot to sender terminals on the gauge. If you got infinity then the gauge resistor is probably open and it wouldn't read.

It sure sounds like the AM gauge is bad. Your test is a good idea. Also running the sending unit wire through a resistor to ground should show a reading on the gauge, which is basically what you're doing to get the 38 ohms.
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Old 08-27-2017, 02:59 PM   #10
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Re: stainless mustang tank, Autometer guage, bad ground?????

My American Autowire Highway 22 fuse panel does not look like a stock one. Again I have a wire that runs directly from the guage to the tank. Nothing to the fuse panel.

I did take the truck on about a 10 mile trip today for lunch and did notice that the guage does move somewhat. What I mean is that when the key is off the needle reads below the empty mark. As soon as you key the ignition the needle comes up to the empty line. I would say total movement of the needle is about 3/8 of an inch. And then goes back down with ignition off.

I wonder if I fill the tank run the sender all the up to it's full position it would release the guage somehow..................Hmmmmmmm.
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Old 08-27-2017, 03:29 PM   #11
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Re: stainless mustang tank, Autometer guage, bad ground?????

Quote:
I wonder if I fill the tank run the sender all the up to it's full position it would release the guage somehow..................Hmmmmmmm.
My money is on NO
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Old 08-27-2017, 06:03 PM   #12
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Re: stainless mustang tank, Autometer guage, bad ground?????

[QUOTE=VetteVet;8026163


I forgot to have you measure ohms from the hot to sender terminals on the gauge. If you got infinity then the gauge resistor is probably open and it wouldn't read.

Would I do this with the wires disconnected? Or with the wires connected and with power on?
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Old 08-27-2017, 08:12 PM   #13
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Re: stainless mustang tank, Autometer guage, bad ground?????

Wires off no power for ohms check. I think you can read the ohms between the end of the sender wire and a good ground if you don't turn the key on.

What is your sender ohms range. The stock chevy truck sender is 0-90 ohms. Zero is empty and 90 is full.
Is the Mustang sender by itself or do you have an in-tank fuel pump with it for fuel injection?
You can check the sender ohms by using the multi meter on the ohms scale and checking between the sending unit terminal and the sender mounting flange with it out of the tank you check it fully down and then gradually raise it up with the meter connected and read the ohms scale.
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Old 08-27-2017, 08:23 PM   #14
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Re: stainless mustang tank, Autometer guage, bad ground?????

Well well well, I just googled the Mustang sending unit and they work just the opposite of GM. The high resistance is empty and the low resistance is full.

Here is the google site that should explain it to you. If you get an Autometer gauge for Fords it will probably work.

http://www.fordification.com/tech/fu...ding-units.htm
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Old 08-27-2017, 08:30 PM   #15
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Re: stainless mustang tank, Autometer guage, bad ground?????

I have the standard ford mustang tank with the hole in the bottom front of tank, and a 75-10 sending unit. I know this because I checked the sender out of the tank before assembly. Only difference in my tank is the fact that it is stainless and I thought that may have been causing a grounding issue. But I think it's the gauge.

I will check the guage as you suggested at the 2 terminals on the backside tomorrow.
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