Gas gauge deflects with turn signal

[Michael J.]

I have a problem with my '63's gas gauge. Not sure it is working as it is on full, but when I use the turn signal, it deflects (down) just like the volt gauge does. Anyone have experience with such things? Thanks.

[Gene M.]

Re: Gas gauge deflects with turn signal

Check grounds. Sounds like one circuit is grounding thru the other.

[Michael J.]

Re: Gas gauge deflects with turn signal

Thanks, I will check the ground wires first.

[David H.]

Re: Gas gauge deflects with turn signal

Mike,

Check tail light ground. I believe both are common. Does your gas gage deflect when you depress brakes? (same ground)

Dave

[Michael J.]

Re: Gas gauge deflects with turn signal

Thanks David, no, no deflection with the brake lights on.

[Ed H.]

Re: Gas gauge deflects with turn signal

Mike, while I was restoring my 57 I read on the tech board that if you double ground the fuel sending unit at it's source
this will preclude the gas gage fluctuation. I used brass end units brass star washers at both ends. I found a location on
on the rear upper of the frame, ground off to bare metal drilled a hole at that location, used #10 wire and a sheet metal bolt, dialectric grease, put
all together and no fuel guage fluctuation. Grounding is the most important function of a corvettes electrical system. I used Lectric-limited
complete wire system and added the grounding touch. Good luck.

[Michael J.]

Re: Gas gauge deflects with turn signal

Thanks Ed, I will try that, I am digging into it as I have time. It is odd that the gas gauge deflects with the turn signal and brake light, whether or not the gas gauge fuse is in or out. With the gas gauge fuse in, it reads full and deflects, with the gas gauge fuse out, it reads empty and still deflects. Usually, with the fuse out, it sits at 1/2. I am also thinking the gauge package may be missing a good ground someplace. I do know the black wire from the sending unit is missing, I cannot see it as it enters the plug under the dash, it should be there with an eyelet to screw into the plate under the door light on the driver's side, this is a tanker sending unit. I will have to search around from the sending unit behind the seat to the plug at the gauge package to see what happened to it.

[Richard G.]

Re: Gas gauge deflects with turn signal

I would pull the spare and tube and take a look. Great time to check the gauge with an ohm meter.
Easy enough to get to and the most likely spot to find an issue.

[Michael J.]

Re: Gas gauge deflects with turn signal

I would pull the spare and tube and take a look. Great time to check the gauge with an ohm meter.
Easy enough to get to and the most likely spot to find an issue.

Fortunately, this is a tanker, so the sending unit is behind the driver's seat. It has three wires coming out as a harness, that then disappears as a wrapped bundle (with the wires from the rear of the car) under the door sill and behind the carpeted kick panel, into a plug that clips on the birdcage. That is the area I am looking now for the ground wire from the sending unit harness.

[Richard G.]

Re: Gas gauge deflects with turn signal

I should have remembered that! (Tanker)
Hopefully you will be able to get to the harness connection and check it there.

[Edward J.]

Re: Gas gauge deflects with turn signal

Hi Mike, I think Gene M. is on the right track, what it sounds like its sourcing your ground to your rear lights because the tank sender ground is open, I would just make up a temporary ground wire long enough to ground the unit, get a couple of alligator clips.

[Michael J.]

Re: Gas gauge deflects with turn signal

Thanks guys, I am making progress. This car was fully restored several years ago, probably by a restorer who was not familiar with tanker sending units. The two wires connected to the back of the gauge are not the two that should be there. One is the switched 12V wire, the other is brown, as it should be, but is a ground wire instead of the wire coming from the sending unit variable resistor. So that explains why it goes to empty when the fuse is out and full when the fuse is in, and deflects with a load like turn signal or brake light. I suspect the brown wire from the sending unit has been crossed with the ground wire. I will get into the sending unit harness from the tank soon and check that all out.