1962 Gas Gauge Puzzle

[Bill O.]

Need your advise as I am stumped.
Symptoms:

• Cold engine, ignition on, gas gauge doesn't register.
• Start motor, runs 30 seconds - 2 minutes, gas gauge registers perfectly.
• Hot engine, ignition on, gas gauge registers perfectly.

Trouble Shooting thus far:

• Wire connections tight on gauge
• Removed brown wire from connector behind driver kick panel, cleaned, reinstalled, checked other connections in adjacent block

I have not removed the tank cover recently but when last there, cleaned, tightened all sending unit connections. Can't be the float because when it sinks it's over.
Can anyone please help...I hate to go in there and replace the sending unit not knowing if that's the problem??????
Thanks much.

[John W.]

Re: 1962 Gas Gauge Puzzle

Bill,

The 18 GA Brown wire runs from the Gauge to the sending unit. If you will lift the gas tank cover and lift the brown wire, turn the ignition switch to the on position. Measure voltage on the brown wire you should have battery voltage. With the wire lifted and clear of any grounds check your gauge to see if it is reacting the same as it does when you first start the cold car. If so you have verified that the brown wire is bringing voltage to the sending unit. Next turn off the ignition and reattach the brown wire. Next jumper the black wire from the sending unit to a good solid grounding point. Preferably the negative battery post if you have a long enough wire. Now turn on the ignition switch and see if the gauge reacts. If so you have a ground problem on the black wire. It goes to your left outboard tail light where it picks up the tail light ground. You may be having issues with your tail lights also if the ground is bad from there back to the frame ground.

If grounding the black wire does not make a difference you may have to revisit the brown wire. If it is compromised somewhere it may be hanging on by one strand. Enough to bring battery voltage to your voltmeter, but not enough to run the sending unit. Test the voltage again on the brown wire connected to the sending unit to verify that it is not dropping voltage along the way. You then would need to jumper from the gauge to the sending unit bypassing the brown wire to verify what you have found.

Good luck. Just remember as bad as the grounding problems are on the old solid axle cars are they are a lot easier to work on than the electronics on the newer Corvettes.

[Roy B.]

Re: 1962 Gas Gauge Puzzle

Your thinking is correct about grounding connections ,that's how the sender works at the gas tank and gage. I think your dash area has a poor ground which gets it's grounding from the engine area some place . I would try running a wire from the battery ground to the dash frame-area some place to see if that does any good. Just a thought

[Bill O.]

Re: 1962 Gas Gauge Puzzle

Thanks John and Roy.

I'm on it !!

[Bill O.]

Re: 1962 Gas Gauge Puzzle

Ground wire from Neg battery post to any metal surface under dash changes nothing.

Question: Since I have a NOS sending unit and since I'll next lift the tank cover and regardless of lead voltage and other ground connection issues should I swap-out the unit while the patient is open?? Maybe I should ground the sending unit/tank to the chassis while in, too; and what gauge wire should I use???

Thanks for all.

[Roy B.]

Re: 1962 Gas Gauge Puzzle

Ground wire from Neg battery post to any metal surface under dash changes nothing.

Question: Since I have a NOS sending unit and since I'll next lift the tank cover and regardless of lead voltage and other ground connection issues should I swap-out the unit while the patient is open?? Maybe I should ground the sending unit/tank to the chassis while in, too; and what gauge wire should I use???

Thanks for all.

You said the gage worked ok so the sender must be OK , I would keep the NOS unit till the old sender went South , OK to add another ground wire and the same size it now uses . You also said the dash gage dont work COLD while you have the tank cover off run a new (Temporary ) wire from the tank ground wire to the gage ground it self while the vett is cold and see if it now works with the key turned on. If it now works you have a bad ground some where els.

[Bill O.]

Re: 1962 Gas Gauge Puzzle

I'll do it. Thanks Roy

Other observations:

• Tail/brake lights work perfectly and burn evenly
• When the gauge is working, turning on the signal lights causes only slight movement of the gas gauge needle "fuller", whereas stepping on the brake sends it to almost "full" (from 1/4 tank).

[John W.]

Re: 1962 Gas Gauge Puzzle

I'll do it. Thanks Roy

Other observations:

• Tail/brake lights work perfectly and burn evenly
• When the gauge is working, turning on the signal lights causes only slight movement of the gas gauge needle "fuller", whereas stepping on the brake sends it to almost "full" (from 1/4 tank).

Bill the only ground for the Gauge is from the sending unit to the tail light ground. The gauge is measuring the current draw through the variable resistor in the sending unit. As the gas level goes down there is less resistance to the electricity going through the sending unit. This increases the current. When you turn on your turn signal you are adding the current from the turn signal to the gas gauge current that is flowing through the ground wire. The connection is not perfect or the wire would handle both without the gauge reacting at all. The brake lights draw twice the current as the turn signal (four bulbs vs two bulbs). This further proves that the ground from your brake lights turn signal is less than perfect. Since the resistance in the bulbs is much less than in the fuel sending unit the bulbs win out and hog about all of the current carrying capacity of the wire.

This all being said it doesn't explain why it would depend on the car being warmed up for a minute or two to get the gauge started.

[Bill O.]

Re: 1962 Gas Gauge Puzzle

John,

New development. Took the little Vette out on the highway today to warm her up. Young lad with a new, very bright blue Honda with a spoiler and a sewing machine motor tried to get a piece of her. He was not happy with the outcome. This little girl burns rubber going into 4th! Sorry, I digress.

Now with less than 1/4 tank, cold motor, switch on, gas gauge works perfectly??????????
I have yet to test volts to sending unit, but based on your recent post does this confirm a grounding problem?? Also, the ground line harness to tail/stop lights goes through body cavity making tracing difficult. Can I run ground line from sending unit directly to chassis and maybe fix/circumvent the problem???

Makes me think we're gettin' closer.

Thanks to all who try to help. And, thanks to Vinnie Peters, read the story about this little Vette in the Summer edition of Corvette Restorer, in your mailbox soon.

[Roy B.]

Re: 1962 Gas Gauge Puzzle

John,

New development. Took the little Vette out on the highway today to warm her up. Young lad with a new, very bright blue Honda with a spoiler and a sewing machine motor tried to get a piece of her. He was not happy with the outcome. This little girl burns rubber going into 4th! Sorry, I digress.

Now with less than 1/4 tank, cold motor, switch on, gas gauge works perfectly??????????
I have yet to test volts to sending unit,dont need to now that it works but based on your recent post does this confirm a grounding problem??YES Also, the ground line harness to tail/stop lights goes through body cavity making tracing difficult. Can I run ground line from sending unit directly to chassis and maybe fix/circumvent the problem???YES

Makes me think we're gettin' closer.

Thanks to all who try to help. And, thanks to Vinnie Peters, read the story about this little Vette in the Summer edition of Corvette Restorer, in your mailbox soon.

Check the ground wire at the tail lights is good , nice to know we helped

[Bill O.]

Re: 1962 Gas Gauge Puzzle

You are up late, my friend.

Thanks a Million,

[Roy B.]

Re: 1962 Gas Gauge Puzzle

You are up late, my friend.

Thanks a Million,

9:40PM this is Ca.

[Bill O.]

Re: 1962 Gas Gauge Puzzle

Touche !
I should'a known.

[John T.]

Re: 1962 Gas Gauge Puzzle

You can and should run a ground wire from the sender to the chassis. Easy to do and should solve the problem.

Good luck

John

[John W.]

Re: 1962 Gas Gauge Puzzle

Bill,

Running a temporary ground from the sending unit to chassis would be a good way to test the grounding issue.

Based on the symptoms I think we may be looking at two problems. Solve one and see if the other one is still there. If it is we may have to continue to solve the mystery.