KDW

Hello my name is Kevin I'm new to forum, it's a pledger to here. I live in So Cal

I currently have a 72 Oldsmobile Cutlass holiday coupe with an original 455 BB that I plan on restoring.
I was wondering if I could get so some help. I read some old post on fuel gauges pegged at ( 3 O clock...)..mine reads empty and when I turn on my head lights than it will to the pegged position ( 3 O'clock..)

Has anyone else had this problem?

Also my temp light looks like it's trying to come ( but not all the way) I know the car can't be hot it has a new water pump, thrums state, fan clutch, water sensor and timing has been checked

I will also need a motor builder soon..someone that's good and I won't have to hock my car just to pay for it.

Thanks

P

Any information would be great...

2blu442

Welcome to the site! The fuel gauge problem sounds like a bad ground to me. It's not too uncommon for the ground wire to corrode back at the gas tank. But since you have other lights on the dash acting up you might try there first. I'm lousy with electrical issues, so if you have time use the search option to look for olds threads discussing bad grounds. If you can't find the steps to take in a previous thread create a post in the Electrical forum with something like "fuel gauge problem" in the title. John

jaunty75

A fuel gauge pegging past the full mark means an open circuit. If it goes to empty, it means either an empty gas tank (duh) or a short in the circuit. The most common problem in old fuel gauge systems is the former, and what 2blu442 suggests (the sending unit ground) is the first thing you would normally check.

However, your problem is weird because the fuel gauge responds to the position of the headlight switch. I'm going to guess that your problem is in the printed circuit on your instrument cluster (the thing the little indicator bulbs screw in to), or, most likely, the connector to the printed circuit, because when you turn the headlights on, power is put to the printed circuit through that connector to illuminate the lamps so you can see the fuel gauge, etc. at night. It's also through the printed circuit connector that both power is put to the fuel gauge and connection to the sending unit in the tank is made.

You might start by just wiggling the connector to the printed circuit. You're going to have to get down under the dash on your back and peer up behind the instrument cluster, but with a flashlight and a little bending of your arm in ways it was never intended to bend, you should be able to see the connector, which is a narrow thing about 2 inches long with a bunch of wires coming out of it, and reach up and wiggle it.

A couple of other questions: do your indicator lights (HOT, OIL, GEN, BRAKE) actually illuminate momentarily like they're supposed to when you start the car? Do the dash illumination lights actually work?

KDW

Thanks for your help....I just went out and checked...the only lights that come on are OIL and GEN....with the key on like your going to start....and yes the dash illumination works

I did climb under the rear and check for ground at tank...the wire is not connect...so I used a pice of wire a tried to ground to bumper still did not work...maybe i need to ground closer to tank over axle?

Any thoughts

Thanks
Kevin
thanks

W70442

Screw that ground wire from the tank straight to the body. There is be a screw hole already there on the vertical surface just in front of the tank toward the pass side if I recall correctly. Just use a self tapping sheet metal screw. You may also need to sand the area down to bare metal so you get a good connection to the body/ground.

To test your gauge...... with the key turned on, disconnect the light brown wire next to the trunk latch inside the trunk. It should be connected to a plug with a pink wire. With that plug disconnected and the key turned on, the gauge should peg past full. If you connect that pink wire to ground/sheet metal with the key on, the gauge should go past empty.
If the gauge responds correctly in both cases, your gauge is most likey ok and the problem is in the sending unit or the wires going to it.

KDW

Hello everyone, thanks for your help. Today I went out and grounded wire from tank and traced lead wire from tank sending unit...this is funny, I guess the old owner connected the License plate light to the sending unit lead. After switching wires and grounding the sending unit the gauge seems to be working...don't know if it's accurate but it's reading.

Also the temp light wire was laying on intake manifold and getting hot, I wrapped it with wire tape and oddly enough lite went off.....does this sound like it could have been the problem?

jaunty75

This explains the connection between your turning on your car's headlights and the fuel gauge changing position at the same time. If there's one thing that's well-known about the infamous "PO" (prior owner), it's that they generally do bad things.

You'll end up determining whether or not your gauge is reading correctly by filling the tank, seeing if it goes to F, and then seeing if it gradually decreases as you drive the car. Just like a good gas gauge should.


The wire getting hot wouldn't mean anything. It's not odd at all that the light would go off after what you did. Those indicator lights (HOT, OIL, etc.) work very simply. When the temperature gets too hot or the oil pressure too low, the switch inside the sensor closes, completing a circuit to ground, and causingt the light to turn on. The standard test of the wiring between the sensor and the dash light is to pull the connector off of the sensor and ground it. The corresponding light on the dash should go on.

Your HOT light was on all the time, correct? That's because it was grounded all the time because the wire was not connected to the temperature sensor, but, instead, was just laying on the engine and making electrical contact with it, thus grounding it.

If you haven't already done so, you should attach that wire to the temperature sensor, and you'll actually have a functioning HOT temperature warning system again.

KDW

Hello everyone thanks for the replys. I'm still having a problem with temp light, after the car is runing for a while...meaning runing temp the light is dim. I replaced the temp sensor, and grounded wire to see if temp comes on..it works and is very bright and blinks...however when I plug it back into sensor it's still dim.

What could cause this?

Any help wound be great

Thanks for your help

jaunty75

It being dim suggests a partial short. The new temperature sensor suggests that the sensor itself is not the problem (although who knows). One small question, and it may be a dumb one, but is the light dim even when you disconnect the wire from the sensor? I'm thinking that there might be a partial short in the wire between the dash and the sensor. When you ground that wire as you did, the circuit is fully closed and the light illuminates brightly. But when you remove it from ground, the partial short might be enough to illuminate it dimly.

If it's off completely when the wire is pulled from the sensor, then all I can think is that you still have some messed up wiring somewhere.

JCervantes

Sounds like you are using a temp sending unit for a gauge not a light

MDchanic

Are you aware that this thread is three and a half years old?

Methinks you are tilting at windmills, sir.

- Eric