The Ford Barn

whb52ford · 08-10-2019, 12:21 PM

My fuel gauge reads full when the car is off. I turn the car on and it drops to between E and 1/4. Stays there all the time. Once in awhile it will read correct, but then drops back.

I replaced the fuel gauge in the dash with a NOS gauge. Same problem.

I found a NOS gas tank sending unit and installed that in the tank. Same problem. I replaced the wire from the gas tank sending unit to the rear of the car where it connects to the car wiring harness. I also ran another ground wire from one of the sending unit hold down screws to the back of the car and grounded it to a bolt. Wanted to make sure I had a good ground. Same problem.

Laying on the floor at the back of the car I ran a negative wire from the battery to the back to the car. I hooked that wire directly to a spare fuel gauge I have. Then I ran a wire from the other side of the fuel gauge to the wire of the gas tank sending unit. I grounded the outside of the gauge. Reads the same.

I took another spare fuel gauge and did the above. Same thing.

Next I took the old gas tank sending unit that is out of the car and hooked it up using the spare fuel gauge. It works pretty much as it should. I pushed the float arm up and it reads full, however it seems to bounce around there. It's not s steady Full. But it appears to be working.

So now I"m thinking that the new fuel tank sending unit is bad because when I test it at the back of the car it is not working. (Shame on me, but I did not test it before I put it in) I'm also thinking that the wire from the back of the car to the ignition switch may be bad. That may be why the old sending unit did not work. The wires are all tight on the ignition switch and the nuts are tight on the gauges at the back of the dash.

Complete wiring harness installed awhile back and fuel gauge worked for many years.

Another note, My oil pressure gauge is not working. When the fuel gauge works, the oil pressure gauge works. Oil sending unit and dash gauge both replaced.

I'm stumped as to what is going on.

JSeery · 08-10-2019, 12:48 PM

Seems like you have several hints there is a wiring issue. If the oil pressure and fuel level both start and stop working together, then I would think that is a wiring problem. And it would be where there is a common connection. Not to be negative, but this is what can happen when you start changing parts without trouble shooting the cause first. It just leads to confusion and frustration. What year car are you working on? A common point to start with would be the ignition switch itself.

whb52ford · 08-10-2019, 01:01 PM

Quote:

Originally Posted by JSeery

Seems like you have several hints there is a wiring issue. If the oil pressure and fuel level both start and stop working together, then I would think that is a wiring problem. And it would be where there is a common connection. Not to be negative, but this is what can happen when you start changing parts without trouble shooting the cause first. It just leads to confusion and frustration. What year car are you working on? A common point to start with would be the ignition switch itself.

It is a 52 Ford car. 6cyl. I did replace the ignition switch a few years back. Had ignition switch out today to make sure the nuts were tight on it. How do you test an ignition switch. Fan, radio, etc all work off ignition switch.

19Fordy · 08-10-2019, 02:20 PM

Since you have an extra fuel gauge , I would suggest buying a 6V dry cell at Lowe's and trying this set up as a test on your work bench. If you know the gauge is good,then problem must be with your sending unit and vice versa.
https://www.fordbarn.com/forum/showt...e+light+switch

Also, check out the wire that is feeding power to the back of your dash gauges.

whb52ford · 08-10-2019, 02:35 PM

Car is 6v positive ground, but I get what you are showing me. That is what I did. What I'm showing is the fuel gauge is good, and the old sending unit is good. But not in the car. When they go in the car, they don't work.

Could be wire from sending unit to wiring harness-that wire replaced
Could be wiring harness to ignition switch-test???
Could be ignition switch-working for radio, fan, etc
Could be ignition switch wire to gauges-both wires tight-

I'm stumped

19Fordy · 08-10-2019, 02:55 PM

Sponsored Links (Register now to hide all advertisements)

Electricity is not my strong point but is you instrument cluster grounded?

Would it be possible to use long pieces of 14 gauge wire with alligator clips at each end and by pass your wiring harness by connecting gauges separately to see if they will work independently?

whb52ford · 08-10-2019, 03:00 PM

Quote:

Originally Posted by 19Fordy

Electricity is not my strong point but is you instrument cluster grounded?

Would it be possible to use long pieces of 14 gauge wire with alligator clips at each end and by pass your wiring harness by connecting gauges separately to see if they will work independently?

I was thinking of using my old sending unit outside the car and see if my in dash gauge moves. Will try that tomorrow.

If that doesn’t work, then I’ll try that.

JSeery · 08-10-2019, 03:45 PM

Quote:

Originally Posted by 19Fordy

Electricity is not my strong point but is you instrument cluster grounded?

Would it be possible to use long pieces of 14 gauge wire with alligator clips at each end and by pass your wiring harness by connecting gauges separately to see if they will work independently?

Did you notice in the OP that the fuel sender works intermtantly and that the oil pressure sender stops working when the fuel sender does? That would point to a common problem.

19Fordy · 08-10-2019, 03:54 PM

I agree.

whb52ford · 08-10-2019, 03:56 PM

Quote:

Originally Posted by JSeery

Did you notice in the OP that the fuel sender works intermtantly and that the oil pressure sender stops working when the fuel sender does? That would point to a common problem.

The only common thing i see is one wire goes to gas gauge, then to oil pressure, then to ignition switch.

JSeery · 08-10-2019, 04:04 PM

I don't have the wiring diagram in front of me, but there should be power to the gauges (fuel & oil). Then there is a wire from each gauge to each sender. The sender provides the ground to the gauge. If both gauges are acting up the problem about has to be in the power to the gauges. Two senders are not going to act up at the same time. There could be a wire issue between the ignition switch and the gauges or some shorting out problem at the gauge cluster itself. It about has to be somewhere in the power to the gauge cluster or at the gauge cluster.

whb52ford · 08-10-2019, 04:19 PM

Quote:

Originally Posted by JSeery

I don't have the wiring diagram in front of me, but there should be power to the gauges (fuel & oil). Then there is a wire from each gauge to each sender. The sender provides the ground to the gauge. If both gauges are acting up the problem about has to be in the power to the gauges. Two senders are not going to act up at the same time. There could be a wire issue between the ignition switch and the gauges or some shorting out problem at the gauge cluster itself. It about has to be somewhere in the power to the gauge cluster or at the gauge cluster.

Maybe I’ll have to pull my dash and replace those wires. Pain, but does make sense. Wonder what would make them go bad. They are pretty protected from everything.

JSeery · 08-10-2019, 05:41 PM

On the wiring diagram there should be a Red/Green wire from the Ignition Switch to the Oil Pressure Gauge and then to the Fuel Gauge and then to the Temp Gauge. So, they are all feed from the same source (Ignition Switch). The wire from the Oil Pressure Gauge to the Oil Pressure Sender should be White/Red, from the Fuel Gauge to the Fuel Level Sender Yellow and from the Temp Gauge to the Temp Sensor(s) Red/White. You could try jumping around each one in turn. I would start by running a jumper wire from the Ignition Switch terminal to the power in on the Temp Gauge and see how it behaves. Then you could move the gauge end of the jumper wire to the power in on the Fuel Gauge and see what, if anything changes, and so on. If it is still behaving strangely, might remove the R/G wire from all three gauges and try the jumper wire again one at a time and see if that makes any difference.

whb52ford · 08-10-2019, 08:42 PM

Quote:

Originally Posted by JSeery

On the wiring diagram there should be a Red/Green wire from the Ignition Switch to the Oil Pressure Gauge and then to the Fuel Gauge and then to the Temp Gauge. So, they are all feed from the same source (Ignition Switch). The wire from the Oil Pressure Gauge to the Oil Pressure Sender should be White/Red, from the Fuel Gauge to the Fuel Level Sender Yellow and from the Temp Gauge to the Temp Sensor(s) Red/White. You could try jumping around each one in turn. I would start by running a jumper wire from the Ignition Switch terminal to the power in on the Temp Gauge and see how it behaves. Then you could move the gauge end of the jumper wire to the power in on the Fuel Gauge and see what, if anything changes, and so on. If it is still behaving strangely, might remove the R/G wire from all three gauges and try the jumper wire again one at a time and see if that makes any difference.

I was thinking tonight. When the car is off, the dash gauge reads full. As soon as I turn the car on it goes to E. What is that telling me. Do I have a short?

koates · 08-11-2019, 02:33 AM

I have read all the above posts several times. Was there a point at some time when all the gauges worked OK. If so then what caused you to mess with something after that. Did you at some time disconnect the wires from the dash gauge terminals and then refit the wires. I am thinking that the power wire from the ignition switch is not on the correct terminal on the back of the first gauge. Its maybe on the sender terminal. Can you read the markings on the backs of all the gauges and make sure the wires are on the correct terminals. Use a good light and a mirror to confirm that all is correct. NO GUESSING HERE, IT HAS TO BE CORRECT. Tell me what are the markings on your gauge terminals. Regards, Kevin.

JSeery · 08-11-2019, 09:29 AM

I'm with Kevin, sounds like something is not correct with the wiring. Another question I have is you said the oil press and fuel gauges are connected to the ignition switch but said nothing about the temp gauge. The wiring diagram has ignition switch to oil pressure to fuel level to temp gauges. And as Kevin posted the terminals have to be correct.

whb52ford · 08-11-2019, 11:57 AM

Quote:

Originally Posted by JSeery

I'm with Kevin, sounds like something is not correct with the wiring. Another question I have is you said the oil press and fuel gauges are connected to the ignition switch but said nothing about the temp gauge. The wiring diagram has ignition switch to oil pressure to fuel level to temp gauges. And as Kevin posted the terminals have to be correct.

I will check to make sure I do have the wires in the dash on in the correct places. I’m pretty sure I do, but think important enough to verify. Maybe Wednesday.

I decided today why not hook up the spare fuel sending unit and see what happens. I just jumpered it it and set it to full tank. I started the car and gas went to full and oil pressure started working. Does any of this make sense?

19Fordy · 08-11-2019, 12:29 PM

That's great news.
It would be interesting to remove the top of the other gas tank sending unit and see it's condition. Clamp it carefully in a vise and use a big screwdriver or brake adjusting tool to pry it off. The little star wheel is for fine tuning the gauge reading, the last photo shows the insides of the fuela gauge. Both are 40 ford but, the same type of King Seally instrumentation is used in your car.

08-10-2019, 12:21 PM	#1
whb52ford Senior Member Join Date: Jan 2013 Location: Ocala, FL 34481 Posts: 235	Fuel Gauge My fuel gauge reads full when the car is off. I turn the car on and it drops to between E and 1/4. Stays there all the time. Once in awhile it will read correct, but then drops back. I replaced the fuel gauge in the dash with a NOS gauge. Same problem. I found a NOS gas tank sending unit and installed that in the tank. Same problem. I replaced the wire from the gas tank sending unit to the rear of the car where it connects to the car wiring harness. I also ran another ground wire from one of the sending unit hold down screws to the back of the car and grounded it to a bolt. Wanted to make sure I had a good ground. Same problem. Laying on the floor at the back of the car I ran a negative wire from the battery to the back to the car. I hooked that wire directly to a spare fuel gauge I have. Then I ran a wire from the other side of the fuel gauge to the wire of the gas tank sending unit. I grounded the outside of the gauge. Reads the same. I took another spare fuel gauge and did the above. Same thing. Next I took the old gas tank sending unit that is out of the car and hooked it up using the spare fuel gauge. It works pretty much as it should. I pushed the float arm up and it reads full, however it seems to bounce around there. It's not s steady Full. But it appears to be working. So now I"m thinking that the new fuel tank sending unit is bad because when I test it at the back of the car it is not working. (Shame on me, but I did not test it before I put it in) I'm also thinking that the wire from the back of the car to the ignition switch may be bad. That may be why the old sending unit did not work. The wires are all tight on the ignition switch and the nuts are tight on the gauges at the back of the dash. Complete wiring harness installed awhile back and fuel gauge worked for many years. Another note, My oil pressure gauge is not working. When the fuel gauge works, the oil pressure gauge works. Oil sending unit and dash gauge both replaced. I'm stumped as to what is going on.

08-10-2019, 12:48 PM	#2
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: Fuel Gauge Seems like you have several hints there is a wiring issue. If the oil pressure and fuel level both start and stop working together, then I would think that is a wiring problem. And it would be where there is a common connection. Not to be negative, but this is what can happen when you start changing parts without trouble shooting the cause first. It just leads to confusion and frustration. What year car are you working on? A common point to start with would be the ignition switch itself.

08-10-2019, 02:35 PM	#5
whb52ford Senior Member Join Date: Jan 2013 Location: Ocala, FL 34481 Posts: 235	Re: Fuel Gauge Car is 6v positive ground, but I get what you are showing me. That is what I did. What I'm showing is the fuel gauge is good, and the old sending unit is good. But not in the car. When they go in the car, they don't work. Could be wire from sending unit to wiring harness-that wire replaced Could be wiring harness to ignition switch-test??? Could be ignition switch-working for radio, fan, etc Could be ignition switch wire to gauges-both wires tight- I'm stumped

08-10-2019, 02:55 PM	#6
19Fordy Senior Member Join Date: May 2010 Location: Coral Springs FL Posts: 10,944	Re: Fuel Gauge Sponsored Links (Register now to hide all advertisements) Electricity is not my strong point but is you instrument cluster grounded? Would it be possible to use long pieces of 14 gauge wire with alligator clips at each end and by pass your wiring harness by connecting gauges separately to see if they will work independently?

08-10-2019, 03:54 PM	#9
19Fordy Senior Member Join Date: May 2010 Location: Coral Springs FL Posts: 10,944	Re: Fuel Gauge I agree.

08-10-2019, 04:04 PM	#11
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: Fuel Gauge I don't have the wiring diagram in front of me, but there should be power to the gauges (fuel & oil). Then there is a wire from each gauge to each sender. The sender provides the ground to the gauge. If both gauges are acting up the problem about has to be in the power to the gauges. Two senders are not going to act up at the same time. There could be a wire issue between the ignition switch and the gauges or some shorting out problem at the gauge cluster itself. It about has to be somewhere in the power to the gauge cluster or at the gauge cluster.

08-10-2019, 05:41 PM	#13
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: Fuel Gauge On the wiring diagram there should be a Red/Green wire from the Ignition Switch to the Oil Pressure Gauge and then to the Fuel Gauge and then to the Temp Gauge. So, they are all feed from the same source (Ignition Switch). The wire from the Oil Pressure Gauge to the Oil Pressure Sender should be White/Red, from the Fuel Gauge to the Fuel Level Sender Yellow and from the Temp Gauge to the Temp Sensor(s) Red/White. You could try jumping around each one in turn. I would start by running a jumper wire from the Ignition Switch terminal to the power in on the Temp Gauge and see how it behaves. Then you could move the gauge end of the jumper wire to the power in on the Fuel Gauge and see what, if anything changes, and so on. If it is still behaving strangely, might remove the R/G wire from all three gauges and try the jumper wire again one at a time and see if that makes any difference.

08-11-2019, 02:33 AM	#15
koates Senior Member Join Date: May 2010 Location: Melbourne Australia. Posts: 2,079	Re: Fuel Gauge I have read all the above posts several times. Was there a point at some time when all the gauges worked OK. If so then what caused you to mess with something after that. Did you at some time disconnect the wires from the dash gauge terminals and then refit the wires. I am thinking that the power wire from the ignition switch is not on the correct terminal on the back of the first gauge. Its maybe on the sender terminal. Can you read the markings on the backs of all the gauges and make sure the wires are on the correct terminals. Use a good light and a mirror to confirm that all is correct. NO GUESSING HERE, IT HAS TO BE CORRECT. Tell me what are the markings on your gauge terminals. Regards, Kevin.

08-11-2019, 09:29 AM	#16
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: Fuel Gauge I'm with Kevin, sounds like something is not correct with the wiring. Another question I have is you said the oil press and fuel gauges are connected to the ignition switch but said nothing about the temp gauge. The wiring diagram has ignition switch to oil pressure to fuel level to temp gauges. And as Kevin posted the terminals have to be correct.