Gas Gauge bench test

[Talarico8447]

How do I test this gas gauge out of the car?  All my previous tests led me to the gauge itself.  Any information is appreciated .        Nick

[Bloo]

1) Figure out how the gauge grounds to the instrument panel. Maybe that brass sheet on back? Anyhow figure out what touches when it is installed. Ground it to a 6 volt battery.

 

2) Figure out which post goes to the sending unit. Hook (+) 6 volts to the post that does NOT go to the sending unit. Gauge should be pegged full.

 

3) Ground the post that would normally go to the sending unit. Gauge should swing all the way to "E".

 

If it will do all that, it is probably ok.

 

If you want to know more, get a sending unit, verify with an ohmmeter that it can swing from 0-30 ohms. Connect it to the gauge. Ground the sending unit frame to the battery. Swing float back and forth.

Edited June 9, 2020 by Bloo (see edit history)

[Matt Harwood]

As someone who is currently suffering through the ordeal of trying (and failing) to get my identical gas gauge operational, I have some tips.

 

If your gauge always reads empty, that means either the sending unit float is sinking, the sending unit is defective, or there's a short to ground somewhere in the wire between the sending unit and the gauge.

 

If your gauge is always full, the wire to the sending unit is broken but not shorting to ground, or the sending unit has lost its ground path, or the sending unit is defective.

 

Test the sending unit wire to the gauge for continuity as well as for a short to ground.

 

The ground for the gauge itself is the brass plate on the back of the gauge (indicated by the arrows). Connect that somehow to a good ground to test. Connecting it anywhere else will smoke the gauge. Ask me how I know.

 

 

The post on the left (when viewing the back of the gauge) connects to the sending unit. The post on the right is +6V power.

 

Be sure to ground your sending unit housing while testing. Connect a wire to the mounting flange and good ground.

 

If you're lucky, it'll be something quick and easy like the sending unit or wires reversed or a bad ground. If you're not lucky, then you're probably me.

[Morgan Wright]

The gauge is a volt meter, and the float in the gas tank is the rheostat that changes the voltage. If you have the float out of the tank, you can hook it up to the gauge and a battery, and lift the cork up and down and watch the gauge read whatever you do to the cork. If the float is in the tank and too hard to get out, you can get a rheostat somewhere and put it in line as if it were the float. I did this and it's a really fun parlor trick to amuse drunk friends.

[Talarico8447]

14 hours ago, Bloo said:

1) Figure out how the gauge grounds to the instrument panel. Maybe that brass sheet on back? Anyhow figure out what touches when it is installed. Ground it to a 6 volt battery.

 

2) Figure out which post goes to the sending unit. Hook (+) 6 volts to the post that does NOT go to the sending unit. Gauge should be pegged full.

 

3) Ground the post that would normally go to the sending unit. Gauge should swing all the way to "E".

 

If it will do all that, it is probably ok.

 

If you want to know more, get a sending unit, verify with an ohmmeter that it can swing from 0-30 ohms. Connect it to the gauge. Ground the sending unit frame to the battery. Swing float back and forth.

 

Thanks for the great list of procedures.

All the tests checked out. The problem ended up being that the gauge itself lost ground contact with gauge housing.

[Talarico8447]

Thanks Matt and Morgan ,

With all this information I have a better understanding how this system works. 😁

[Matt Harwood]

1 hour ago, Talarico8447 said:

 

Thanks for the great list of procedures.

All the tests checked out. The problem ended up being that the gauge itself lost ground contact with gauge housing.

 

That appears to be the problem in my car as well. How did you remedy it?

[Talarico8447]

The back of the gauge housing where the gauge sits and makes contact was grey and powdery. I scuffed it up with 0000 steel wool until it was fresh metal again then tested the assembled gauge with lead wires before I put it back in the dash.  I think just from sitting for 80 years the metal kind of corroded. Looking back I should of taken a picture of the back of the housing. 

        When you put it back together make sure the Ivory plastic is not pressing on the needle. Test it opened and assembled before you put it back in the dash.

I learned the hard way.