fuel gauge

[Don 42616]

why all of a sudden does my gas guage 67 jerk around so much? Just started..I wonder if wires are shorting? But, I think a fuse would blow. Ideas?? Thanks ,Don

[Roy B.]

Re: fuel gauge

Run a good ground to the gage and see what happens

[Jack H.]

Re: fuel gauge

Mid-year gas guage circuit is unique. The pointer needle is held in position by two opposing electro-magnets pulling it in opposite directions with the relative strength of each magnetic field dictated by the position of the float in the tank. If the gauge needle is erratic, then it's being 'told' to point in different directions!

For good steady gauge readings, all electrical contacts need to be in good repair (oxide free), the interconnect wiring needs to functionally intact (no skinned wires sproadically shorting to ground) and the grounds need to be solid.

Notice I used the word ground in plural! Yep, I intended to because in the unique mid-year configuration of the gas guage, a Wheatstone bridge circuit topology is used. Forget the fancy electrical engineering buzz word--it means the pointer needle's position is INDEPENDENT of the absolute voltage powering the circuit and only depends upon the voltage divider relation established by the electro-magnets in the gauge and the resistance ratio of the sending unit in the gas tank.

BUT, to make this 'neat' feature work BOTH the gauge and the sender have to be grounded and those grounding points have to the SAME. So, if there is oxidation/corrosion at the grounding wire between the frame and the tank sending unit, you've got a problem. Same goes for the gauge itself. If it's not bolted FIRMLY to the instrument cluster OR the instrument cluster's gounding is 'flakey', you'll see all kinds of funky problems.

[Don 42616]

Thank you Jack Humphrey.

I can see the results when you pointed out the opposing magnets. Now I have to figure out where the oxidized wire is. Don

[Don 42616]

Re: fuel gauge thanks Roy I will try it . NM *NM*

[William C.]

Re: Thank you Jack Humphrey.

look at the ground connection at the sending unit first, make sure the terminal on the sending unit and the connecting trrminal are clean and free of corrosion products, paint and whatever.

[John H.]

Re: Thank you Jack Humphrey.

The ground wire at the '67 sending unit has no direct connection to the frame; it's spliced into the rear harness (along with the grounds for ALL the rear lamps) and runs forward, through the body connector above the left kickpad, and from there it's spliced again to pick up the clock ground, then grounds in two places - at the cluster ground spade, and grounds common with the radio ground (second wire in that connector cavity) at the screw into the lower dash brace. Lots of potential for less-than-optimal connections before it finally gets to ground.