The fuel gauge needle on my 68 firebird reads way past the F mark. I am trying to figure out if its the sending unit or the gauge. I was wondering what voltage the gauge was supposed to have when the tank was full. I was also wondering if there was any way to check the gauge using an ohm meter. Any information would be helpful. Thanks

Welcome to the group. The sender is a variable resistor. When its full I think it should be 90 ohms. When the tank is half filled what is the guage showing? Is the problem just when its full or is the whole scale off?

Welcome, I dont want to hijack your thread, but I am also wondering about how to test the fuel gauge if the sending unit is ok?
I know you can ground the sending unit wire (brown wire) and the gauge should go to empty but what tests can you do on it other than that?
My gauge also reads all over the scale, not just from Empty to Full. What does this indicate?

When I bought my car the fuel gauge didnt work, got a new sending unit...now works.
it always shows partly beyond full when full, ...not sure when its empty yet, because I always fill up when it shows 1/4 full. but then I can put about 9-11 gals in it...so in other words , they are not very accurate..

I can tell you from experiance - when mine says empty - it is empty.

I have coasted into a gas station twice.

Also try testing your ground first. Look for a black wire and ground point at the front of your gas tank.

Mine reads 3/8 when full and 8:00 when empty. It's been that way since I got it. I even replaced the sender with no change. One of these days I'll trouble shoot it. I don't know if it is a resistance problem or the gauge is spun in the housing.

The needle seems to usually sit at the 3:00 position. It will sometimes move down below the 1/2 mark. Thanks everyone for your replies.