fuel level gauge & sending unit help

[pegleggreg]

I have a problem. I keep running out of gas. I have a fuel cell with a fuel level sending unit. But the prior owner had a wire from the fuse block to the sending unit & no ground wire to the sending unit at all. While i was chasing the wire from the sending unit to the fuse block i noticed a couple cuts in my carpet on the floor board. Also some melted wire, so obviously there was a problem. I am no electrician, but to me, it is not safe to run a hot wire to the gas tank. So i disconnected the wire. Does anybody know the correct way to wire up the fuel level gauge to the sending unit? It reads resistance i think.

[VetteVet]

It is very helpful to indicate some details about your vehicle because there are differences in the years and it keeps the guessing game down some.
Try this link. DO NOT PUT ANY HOT WIRES TO THE TANK SENDING UNIT!!!! You might burn down your truck. You may not have the sending unit flange grounded I.E. the tank may not be grounded back to the battery negative through the frame.

http://www.6066gmcguy.org/Electrical-02.htm

[pegleggreg]

My vehicle is a 1969 Chevy C10 w/ a 357 & turbo 350. I have all factory gauges and a fuel cell. I checked the terminal where sending unit was wired to and there is no power in the on/off position. So there was not a hot wire leading to my tank...Thank God! Although it looks as if that was a problem for the prior owner of the truck. But now does te circuit board behind the instrument cluster supply the 12v to the gauge, or do I have to run a wire to the gauge? If so, which side does the hot wire go to?

[VetteVet]

Originally Posted by pegleggreg

My vehicle is a 1969 Chevy C10 w/ a 357 & turbo 350. I have all factory gauges and a fuel cell. I checked the terminal where sending unit was wired to and there is no power in the on/off position. So there was not a hot wire leading to my tank...Thank God! Although it looks as if that was a problem for the prior owner of the truck. But now does te circuit board behind the instrument cluster supply the 12v to the gauge, or do I have to run a wire to the gauge? If so, which side does the hot wire go to?

Yes the printed circuit supplies the connections to the fuel gauge. The wiring harness connects the power and grounds at the plug in, on the back of the gauge panel as shown in the pic below. Disregard the red wire, it is a tach connection but that is the fuel gauge power that it is connected to.
You can check the fuel gauge easily by just grounding the terminal in the fuse panel just below the hazard flasher. I think you know where it is. When you ground it with the key on you should see the gauge needle move to the left below empty. If you dont have a connection from the sending unit to this terminal and the fuel gauge has power it should read all the way to the right past full. If you get no reading then the gauge is bad or it's not getting a connection.



You can check the sender unit by measuring the resistance between the tan wire terminal connection and the sending unit flange. You should see between 0 and 90 ohms depending on the float position. Check the sending unit flange to the tank and you should get zero ohms. Be sure the tank is grounded to the frame. I hope it isn't a polyurethane tank or you will have to run a separate ground wire to the sending unit flange.
Have you checked the link I posted above and also check other threads in this forum as there are many on the gas gauges.

[pegleggreg]

Alright great, u have answered my question. I will try this and let u know. Thanx!

[pegleggreg]

Ok I checked the fuel gauge terminal on the fuse block and I get around 50 ohms. Same in the on or off position. I grounded the fuel terminal on the fuse block and the gauge didn't move. I checked the fuel sending unit flange to tank and it pegged the ohms meter. I checked the ground to the sending unit wire and I get 50 ohms. Idunno? From what u tell me, that if I ground the fuel terminal on the fuse block, the gauge should drop below empty. So my gauge may be bad. Also u said if i check the sending unit flange to the tank, I should get 0 ohms. But the flange is metal and so it the tank and the flange screws are metal so there would be continuity there for sure. So I am lost now. Tell me if I am reading or doing something wrong.

[VetteVet]

My replies are bold.

Originally Posted by pegleggreg

Ok I checked the fuel gauge terminal on the fuse block and I get around 50 ohms.This is about right. Same in the on or off position.
I grounded the fuel terminal on the fuse block and the gauge didn't move.With the key on it should go below empty.
I checked the fuel sending unit flange to tank and it pegged the ohms meter. This means the sender is grounded to the tank, thats good and is the tank grounded to the frame? I checked the ground to the sending unit wire and I get 50 ohms.If this is the tan wire that goes to the tank it means that you are reading through the sender to the tank and that translates to a little over 1/2 tank of gas.
Idunno? From what u tell me, that if I ground the fuel terminal on the fuse block, the gauge should drop below empty. With the key on. So my gauge may be bad. Also u said if i check the sending unit flange to the tank, I should get 0 ohms. But the flange is metal and so it the tank and the flange screws are metal so there would be continuity there for sure. Right I agree.
So I am lost now. Tell me if I am reading or doing something wrong.

From what you are telling me you are not getting power to the fuel gauge or the gauge is Kaput. When you unplugged the tan wire from the fuse block you isolated the fuel gauge from the tank and when you grounded the terminal on the fuse block the gauge didn't move, however you read resistance on the fuse block terminal. This means that the gauge is getting continuity from the fuse block on the ground side. You now have to check the positive side for voltage. Are your other gauges working since they are all
powered by the same source.?

[pegleggreg]

You sure do know your stuff on electrical and these instrument clusters. I thought the gauge was bad but it was really just an operator error. I looked at the pictures and the link that u sent me & I hooked the wires up. But I was being dyslexic. After I realized that I had the wires on the wrong spot on the gauge, I reversed them and then the gauge was working just fine. Thank You very much for all your help and patience. You knew what I did wrong before I got a chance to read your reply. It is good to know that if I ever have any other electrical issues in the future, I have someone to ask questions too. Thanks again and I am sure we will chat sooner or later. Lol.

[VetteVet]

You're very welcome.

[rbeau30]

Sorry to resurrect this thread, but it has a lot of good info on it.

I did not see the below scenario in the thread and I want to see if anyone has some suggestions as to my conclusion on what is wrong with my fuel guage reading.

When my sending unit wire (brown) is plugged into the sending unit, my guage reads <Empty>. When I unplug the brown wire from the sending unit my guage needle immediately goes to <Full>. What I am deducing from my research on the internet and here is that I have a bad sending unit or the float is stuck in the down position (bad float maybe?)

Is it really hard to remove the sending unit from the tank to check the operation of the float?

[VetteVet]

What you are seeing is normal. This is the best way to check the gauge.
Your conclusion is correct but it may also be a grounded tan wire to the sender. If you pull the tan wire off at the sender and the gauge goes past full then it indicates that the problem is in the sender unit.If the gauge continues to read empty then the tan wire is grounded to the truck floor somewhere. It is not hard to get the sender out if the tank is behind the seat.
Obviously you have some gas in the tank?

[rbeau30]

Originally Posted by VetteVet

What you are seeing is normal. This is the best way to check the gauge.
Your conclusion is correct but it may also be a grounded tan wire to the sender. If you pull the tan wire off at the sender and the gauge goes past full then it indicates that the problem is in the sender unit.If the gauge continues to read empty then the tan wire is grounded to the truck floor somewhere. It is not hard to get the sender out if the tank is behind the seat.
Obviously you have some gas in the tank?

Thanks for your reply VetteVet, btw TSgt USAF active duty here, when did you retire?

Ohhh yes, I have gas I bought the truck with the gauge malfunction. Definately have gas in the tank. I followed the tan wire all the way to the fuse box it looks relatively new and just fine. Perhaps the PO replaced it to see if that worked because the way the wire is routed, it looks like it is prone to corrosion.

I can double check though with my multimeter to find out if the float is returning a resistance (I am pretty sure I have about a half tank should give me between 0 and 90 ohms but close to about 50), by clipping one end of the multimeter on the post of the sender unit, and the other to a ground nearby. I am theorizing this should tell me if the sending unit is malfunctioning, and/or if the tank is properly grounded right?

I think I have read on a couple websites that you need a wrench to get the sending unit out of a stock gas tank that is behind the driver seat? Is there any other suggestions on how to get it out? I really hate buying uni-taskers.

[clinebarger]

Pull the sending unit and see if the float has filled with gas giving an empty reading. i have had this happen dozens of times.

[VetteVet]

Originally Posted by rbeau30

Thanks for your reply VetteVet, btw TSgt USAF active duty here, when did you retire? 1 Sep 04 and loving every minute of it. A-10 crew chief

Ohhh yes, I have gas I bought the truck with the gauge malfunction. Definately have gas in the tank. I followed the tan wire all the way to the fuse box it looks relatively new and just fine. Perhaps the PO replaced it to see if that worked because the way the wire is routed, it looks like it is prone to corrosion.

I can double check though with my multimeter to find out if the float is returning a resistance (I am pretty sure I have about a half tank should give me between 0 and 90 ohms but close to about 50), by clipping one end of the multimeter on the post of the sender unit, and the other to a ground nearby. Check from the post to the flange of the sending unit. This checks the sending unit resister, SB between 0 and 90 ohms. I am theorizing this should tell me if the sending unit is malfunctioning, and/or if the tank is properly grounded right? Check between the sender flange and a nearby ground, grounding isn't the problem, either the float is stuck on the bottom of the tank and reading zero ohms to ground or the tan wire is grounded, and I have seen the post assembled directly to the flange and not insulated from it.

I think I have read on a couple websites that you need a wrench to get the sending unit out of a stock gas tank that is behind the driver seat? Is there any other suggestions on how to get it out? I really hate buying uni-taskers.

Just use a couple of screwdrivers as levers and rotate it, and it should come out

[caboutin]

Any hints on how to tighten the new device so that we don't smell gas all the time. :]

[Hitman_Motorsports]

im having the same issue with my fuel gauge in the truck. I fill the gas tank and the gauge wont move. so i need to know , how to "ground" out the fuse. is that a wire from the fuse terminal itself and grounded to bare metal? then a stupid question. I have a switch on the left hand side on the floor, im assuming the gas tank . it has a m l r on it. Im assuming a main , right tank left tank? How do i fill these tanks? Do i do this individually? My gas tank is behind my seat and i dont know where a reserve would be.

by the way i have a 71 chevy c-10 long bed all stock

[WIDESIDE72]

I too am chasing fuel gauge gremlins. None of my dash lights work even though I replaced all of the lamps when I cleaned up the cluster before install. Problem is It is a factory tach dash i added so i dont know if it worked or not. The printed circuit looked good but I suppose I need to check it with my meter.

I have already installed a new brake light switch, neutral safety switch and turn signal switch. A month or so ago when I installed everything, the only thing that worked on the first try was the horn but when I went to use it today, it wouldnt work!

[VetteVet]

Please do me a favor and start a new thread with this post so the new guys don't have to wade through all the posts above and especially since you may have multiple problems. I may have to post some diagrams as well. Thanks

[twoskies]

hi, 1971 c10, all dash lights work, no fuel gauge, no dome light, is there supposed to be 12 volts at the tan sending unit wire?, ive got no voltage on either end(fuse block or plugin on sending unit, dome light has 12 volts on white wire but doesnt work, any help appreciated, thanks

[VetteVet]

Originally Posted by twoskies

hi, 1971 c10, all dash lights work, no fuel gauge, no dome light, is there supposed to be 12 volts at the tan sending unit wire?, ive got no voltage on either end(fuse block or plugin on sending unit, dome light has 12 volts on white wire but doesnt work, any help appreciated, thanks

If you will go to the top of this page and click on forum tools at the top of the page then click on new thread, and copy/paste this post in the 1st post I will help you with your problems.

[twoskies]

hi, i dont have a dropdown in forum at top of page, do i need to pay to post new posts?, that would not be a problem, thanks

[VetteVet]

Originally Posted by twoskies

hi, i dont have a dropdown in forum at top of page, do i need to pay to post new posts?, that would not be a problem, thanks

Sorry I forgot to mention you need to go to the main page of the electrical forum, or any other forum you want to start a new thread in, and look on the top left, where you'll see a box to click on that says "new threads".

No you don't have to pay to post unless you' re trying to sell something.
At the bottom of this page is a dropdown that shows all the forums. Just click on the arrow and it will list them then select the one you want to start a new thread in, then click go.