# PLEASE HELP II - Only one thing left to fix - gas gauge



## 70455goat (Nov 5, 2007)

This forum is GREAT!!! I got my shifting problem fixed thanks to Rukee and Geeteeohguy. YEAH!!!

Now I have one last thing that I can't seem to get to work right. The gas gauge will move to a spot and just stay there. When I filled it up for the first time, it went to full, and I thought great, it's started working. Only next week it was still on full and the next week.....I put gas in it the other day and it went to half and now its stuck there.

Any ideas????

I wanted to take a look at the gas tank to see if maybe a wiring connection needs to be cleaned or loose, but I don't see any wires going to the tank. There's one that comes out from on top of the tank on the front side that is grounded next to the tank. I also wiggled the wiring harness where it connects to the gauge cluster, under the dash to see if maybe something was loose there and no change to the gauge.


----------



## Rukee (Feb 8, 2007)

Awesome! :cheers
I`m not sure were the sending unit comes out on your tank, but there should be two wires attached to it. There is the one you aready see that goes to the ground and the second goes up to the dash. If your able to disconnect the dash wire, with the key on the gauge should go to empty, grounding that wire should make it go past full. Hooking up a test light to the wire with the light grounded should yield a half full gauge. IF you can get your gauge to react like described then the problem is in the tank`s sending unit. IF you can not get the gauge to react like described then the wiring or the gauge is at fault.


----------



## 70455goat (Nov 5, 2007)

Rukee said:


> Awesome! :cheers
> I`m not sure were the sending unit comes out on your tank, but there should be two wires attached to it. There is the one you aready see that goes to the ground and the second goes up to the dash. If your able to disconnect the dash wire, with the key on the gauge should go to empty, grounding that wire should make it go past full. Hooking up a test light to the wire with the light grounded should yield a half full gauge. IF you can get your gauge to react like described then the problem is in the tank`s sending unit. IF you can not get the gauge to react like described then the wiring or the gauge is at fault.


Thanks for the info. I did not see any other wires going to the tank. I know there has to be another wire somewhere. I'll take another look tomorrow.

Dale


----------



## 05GTO (Oct 6, 2004)

The gas tank wire is in with the ribbon cable that is under the drivers seat (on 66 and 67) the wire feeds thru the car just above the differential. On my 66 If that wire is unpluged the gauge shows full.


----------



## Rukee (Feb 8, 2007)

hmmm.....did I get that backwards?? I think I did. 
In any case, you should be able to manipulate the gas gauge with that wire between ground, open and part resistance through a test light.


----------



## 70455goat (Nov 5, 2007)

Thanks guys. I will work on the gas gauge tonight. With no gas gauge and a 455, I'm afraid to drive it without putting gas in every time I drive!


----------



## 70455goat (Nov 5, 2007)

Rukee said:


> hmmm.....did I get that backwards?? I think I did.
> In any case, you should be able to manipulate the gas gauge with that wire between ground, open and part resistance through a test light.


Rukee, I found where the wire comes up into the rear part of my trunk. There is a connector right by the trunk latch. I disconnected it and attached the wire going to the dash to ground, and it went straight to full. So you were correct. Ground equals full tank!

One thing is different though. When I disconnect the wire, the gauge just stayed where ever it was last sitting. When I started testing, my gauge was showing a half tank. It went to full with a ground put on it and when I connected the wires back, it went back to half.

I am pretty sure the gauge is okay. You said to put a test light between the tank and the gauge and it should read half. When it went to full, I disconnected the wires and it stayed full. I put two wires on a dome bulb and inserted it between the gauge and tank. Still stayed on full. Hooked connections back together and it went back to the original half tank.

Getting there....any more ideas?????

Dale


----------



## Rukee (Feb 8, 2007)

The test light should go between the gauge and ground, not the gauge and the tank. And you should get a reaction or a gauge change with each, open wire, grounded wire, and part resistance through the test light.


----------



## 70455goat (Nov 5, 2007)

Rukee said:


> The test light should go between the gauge and ground, not the gauge and the tank. And you should get a reaction or a gauge change with each, open wire, grounded wire, and part resistance through the test light.


Okay Rukee,

Let me see if I understand how this circuit works....

At the tank end, the circuit starts from a wire that is grounded behind the tank, that wire goes to the sending unit in the tank and continues to the gauge. Now this is where I am lost, because you said the test light should go between the gauge and ground (not the gauge and tank). Shouldn't there be 12VDC on the other side of the gauge? I wouldn't think it would work with grounds on both sides??????

Thanks,
Dale


----------



## Rukee (Feb 8, 2007)

The gauge works with two connections, a positive 12VDC to keyed ignition and a ground. The 12VDC is on the gauge itself and the sending unit in the tank manipulates the ground. So when you pull the wire from the tank it`s a ground wire you have there. Connected to nothing the circuit is open or 0% resistance, connected to the frame it`s grounded and 100% resistance and connected to a test light to ground is 50% resistance. You should see a over full, empty and half full gauges when testing. Hope this helps.


----------



## 70455goat (Nov 5, 2007)

Rukee said:


> The gauge works with two connections, a positive 12VDC to keyed ignition and a ground. The 12VDC is on the gauge itself and the sending unit in the tank manipulates the ground. So when you pull the wire from the tank it`s a ground wire you have there. Connected to nothing the circuit is open or 0% resistance, connected to the frame it`s grounded and 100% resistance and connected to a test light to ground is 50% resistance. You should see a over full, empty and half full gauges when testing. Hope this helps.


That is exactly how I thought the circuit works.

I am still working on the gauge. I made a mistake in one of my previous posts. It does go empty when I put the wire in the trunk to ground and full when I disconnect it. I must have been on crack the other night!

I have determined that the gauge is working perfectly. now I just need to narrow it down to wiring between the connection in the trunk and the ground on the other side of the tank/sending unit. It is continually going back to half tank when I put the connection back together. I am hoping that it was just that connection was faulty and me disconnecting and reconnecting it fixed the problem. Next time I put gas in, I am going to stop every few gallons and turn the key on to see if if moves up correctly.

Thanks for all of your help.


----------

