1957 chevy gauge cluster issue

[57chevy3100]

I pulled the old gauge and replace it with a new one.
I am having an issue with what seems to be a grounding issues.
If I using an ohm meter both side of the fuel gauge and the temp gauge read
a direct ground to the gauge frame itself. When I hook up the power wires, one to the power side and the other from the gas sender unit, I can read 12 VDC from the frame of the gauge cluster to ground.
This is strange, as the old one reads the same.
I looked and insulators etc, all good and the new one looks the same.
Ideas???
I can send pics too

[VetteVet]

Originally Posted by 57chevy3100

I pulled the old gauge and replace it with a new one.
I am having an issue with what seems to be a grounding issues.
If I using an ohm meter both side of the fuel gauge and the temp gauge read
a direct ground to the gauge frame itself. When I hook up the power wires, one to the power side and the other from the gas sender unit, I can read 12 VDC from the frame of the gauge cluster to ground.
This is strange, as the old one reads the same.
I looked and insulators etc, all good and the new one looks the same.
Ideas???
I can send pics too

One thing you need to keep in mind is that when checking voltage you are reading the voltage potential between positive and ground. Just like when you read the voltage on a battery between positive and negative,

The measurements you are taking are between positive and ground on the fuel gauge. It will be whatever the battery voltage is, unless a current is flowing through a resistance to cause a voltage drop on the load. You can see this better by looking at the diagram below.




Looking at the gauge you can see the positive input from the key switch and the path of the current between there and the end path on the sender and the ground on the gauge cluster.

If you look at the gauge, you can see the coils that deflect the needle between Empty and Full, and the connection between the gauge input and the sender wire to the tank, and through the sender resistor to the sending unit and tank ground.In each case there is a path from positive to ground.

If you are reading Ohms or continuity on the gauge through the same paths, you should get a small reading as the voltmeter sends a tiny current through the paths from positive to negative (ground). If there is any resistance it will be small in the needle coils, and usually around 45 ohms on the gauge resistor between positive and sender terminals, and more if you read from positive all the way to the tank sender body.

If you read zero ohms on either path, you have a direct short between positive and ground and it will flow as much current as the coils and resistors and the wiring will allow before they burn into. Are you sure that you are not getting a resistance reading on the meter? If you are getting a very small reading it still might look like a short but be enough to be normal.