[64speed]

How do I test my gas gauge?

[John V.]

I think the procedure is in the Shop Manual (mine not accessible at the moment).

This video provides a good primer on checking the sender and gauge for function.

https://www.youtube.com/watch?v=7jNJEYcAayA

You can also find a video if you want to check the ohm range of the sender.

If you're not aware, the '64 sender used a different ohm range than the '65.

You won't get an accurate gauge reading if the sender's ohm range isn't matched to the gauge.

In simple terms, the gauge responds to voltage thru the sender's variable resistance. The sender's resistance is dependent on the float position of the sender in the tank. Depending on how much resistance the sender provides, the gauge responds by reading that resistance (actually it detects the voltage which varies according to the resistance) to indicate the appropriate fuel level.

I am not certain if maximum resistance corresponds to full or empty in the '64 system, it would be one or the other. IIRC, the ohm range of the '64 sender is 0-30 ohms, I'm sure somebody will correct me if I'm wrong.

Since you've asked, I assume you have a problem. What does the gauge read? That might give a clue as to what is at fault. Was it working and then stopped working?

If you want to bench test the gauge, you could hook up a ground for the gauge and a 12V power source for the gauge and then use the sender or a variable resistor (0-30 if that is correct) and see how the gauge responds as you vary the resistance thru that range.

But that seems way complicated unless the gauge is already out of the dash.

As the video suggests, check your wiring as that is the most common problem for a gauge reading issue.

[64speed]

The car is not wired up and the dash is out. I want to test it before I assemble the dash. I don’t even know which terminal is positive/negative, and yes it is 30 ohm

[John V.]

I'm no electrical whiz but I believe as long as it's an isolated DC circuit I don't think it matters which side is grounded and which side is positive (in the car it does matter since all circuits share a common negative ground).

However, in the case of a '64 gas gauge, there are three terminal posts on the back, right? Not sure what would happen if you wired it up wrong so don't take my advice as the final word. Might fry the thing.

There are 2 terminals side by side and angled to each other.

The 3rd is at the bottom and it is the ground terminal.

The 2 terminals side by side is where you would plug the V shaped 2 wire connector to the gauge.

Per Pete Serio, the '64 connector was ivory color (the '65 was changed to black).

The angling of the terminals and the V shaped connector made it impossible to screw it up at the factory, the connector only fit one way.

One of these terminals is the 12V power source and the other is the wire coming from the Sender.

Since they designed it so that you couldn't reverse the wires, it is either important that the wiring is connected to the proper terminals or perhaps it simply would make the gauge read "backwards", empty when full and full when empty. Or maybe the gauge wouldn't work at all. As I said, electrical is not my strength although I can follow a circuit diagram pretty well.

The Wiring Diagram in the Shop Manual would tell you which wire came from the Sender and which one from Power (I suspect from the ignition switch).

Check this thread. The last couple posts relate to connecting a '64 sender connector to a '65 gauge.

https://forums.maxperformanceinc.com...d.php?t=656581

Pete Serio says that you have to switch the wires in the '64 white connector to make the '65 gauge work. That suggests to me that the '65 gauge reversed the position of the power and sender wires.

I am guessing that the pics he posted show the '65 black connector as factory wired along with a '65 gauge and assuming the terminals look the same on the '64 gauge.

If I was guessing, I think the Sender wire is likely the Brown wire.

If the '64 used the same color wires, then the '64 gauge should have the Brown Sender wire on the opposite side as compared with where it is on the '65.

Looking at the BACK of the '65 gauge, I think the Sender wire would be the Brown one and connected to the right side terminal and 12V power to the left side terminal.

Assuming I am interpreting the post correctly, the '64 gauge connector would connect the Brown Sender wire to the left side terminal.

If you were fearless, you'd try that and if the gauge didn't respond, just reverse them.

Or take the smart approach and PM Pete Serio and see what he says!