Another GAS gauge question/problem

[Kahuna]

My friend has a 52 Mercury. Car is converted to 12 volts.
The original fuel tank sender was bad and was replaced
with a new one from a place called Concourse Parts. The
original gauge is still intact.
After installing the new sender, making sure the grounds
were proper, the gauge reacts:
But, with a 1/2 tank of fuel (19 Gallon tank), the gauge
moves to 1/4, then slowly moves back to the empty side.
I'm told the sender was adjusted properly.
The gauges are original and an IVR is used to work with the
12 volt system.
Any insight, suggestions appreciated
Jim

 

[JSeery]

The new sender is most likely a resistance type, the original system is a current pulse type system. Points in the sender open and close to control the current flow. It is hard to match the proper current flow with the resistance sender. If you want it it work as designed, I would have an original sender repaired.

 

[mrtexas]

You can also send your meter off and have it converted to resistance type.

 

[19Fordy]

K: There are those who disagree, but the newer resistance type sending units will not accurately work with the original gauge. A SEARCH will reveal volumes of experiences. The interior of your sending unit looks like this.

 

[Kahuna]

Thank You Boys. I was suspecting this, but was totally unsure.
I will relay the info
Jim

 

[Flat Ernie]

K: There are those who disagree, but the newer resistance type sending units will not accurately work with the original gauge. A SEARCH will reveal volumes of experiences. The interior of your sending unit looks like this.

I'm one of those who disagree.

I have used the aftermarket senders on a couple vehicles that have been converted to 12V with no issues.

Based on original poster's comments, I suspect the sender was not adjusted properly. I'm also not a fan of the chopper 6V regulators.