Gas Gauge

[extremesounds13]

I did some searching and couldn't find an answer. The gas gauge in my seventy burb is always on empty and I want to fix it. I unplugged the brown wire that comes from the gauge and plugs into the fuse box and the gauge goes to about the three o'clock position. So my assumption was is they wire coming forward was grounded. So I went to the tank and as close as I could I cut the brown wire and then ran a new one up to the wire that was unplugged from the gauge and nothing changed it stayed a three o' clock. In fact even if I ground the wire going right to the gauge it stays at three o'clock too, but as soon as I plug it back in the fuse box it goes to empty. So what am I doing wrong? Is the brown wire not the right one going back to the tank. Or what else could it be?

[vectorit]

Just a few questions off the top of my head at this point, assuming that your float is ok and we are focusing on wire.

Have you made sure that the rear harness hasn't been butchered by trailer lights or has been pinched by the body? (Check to see if the fuel gauge wire has been mended, then over time come loose).

Have you separated the rear harness connector and tested the continuity from the connector back to the tank connector? (Isolate the rear harness).

Also, have you run a scrap wire from the negative terminal of the battery to the tank? (Testing good ground).

Finally, looking in the passenger side rear wheel well. Look at the top of the tank, and see if the connector is still in good shape. It's a rubber boot, that has a brass snap terminal inside it. This connector fits over a pin, then snaps onto it. You will have to take a thin long probe to get to the connector, then move it around while someone looks at the gauge. See if the gauge responds to you moving it.

[Steven B]

Chances are the float has sunk.

[dougo]

Mine just started to act up this week on my burb... it now reads empty, or close to empty. Needle no longer moves. I was thinking fuel sending unit, or float. I have not had time yet to trouble shoot...

[dubds10]

Mine moves from empty to 1/4 full and never more, even on a full tank lol Damn old chevy gauges. For how much gas this truck sucks back though, I'd be afraid to see how fast it'd move if it actually worked properly

[AzDon]

Mine was working, now it's not! Previous owner cut a hole in the floor to work through.... If I take the wire from the sender and touch it to ground, gauge goes to full while wire completely disconnected registers empty. Gauge is stuck on 1/8 with wire connected.
I've proven to myself that from the sender forward everything is working, so it is a sender problem. The idiot that cut the hole didn't quite cut it far enough right for me to pull the sender and a hitch was WELDED under the tank..... Dontcha just love the modifications you find on used stuff?

[extremesounds13]

worked with it again today with no luck, does anyone have a diagram on the wiring? How many wires go into the sending unit, I think I only see two a red and a brown and the brown I am assuming is going to the front?

[vectorit]

It's late, and I am fuzzy.. But, IIRC there is only one wire to the sending unit.
Hence why grounding is important.

You should be able to trace the wire to the underside of the driver side tail light area, from under there is a hole the wire for the tank and the license plate come out. Make sure they are still intact, since that area gets rusty and jagged.

From the inside, pull the driver side rear panel to expose the tail like region. Make sure all is ok there, then if you do not have a headliner the loom traverses the driver side. You should be able to dig it out with your hand, then inspect it all the way to the A pillar for chafing.

[72freak]

Have you pilled the sending unit and put a multi meter on it?

[extremesounds13]

Originally Posted by 72freak

Have you pilled the sending unit and put a multi meter on it?

I figured that would be my last resort as it would require dropping the tank.

[70LonghornCST]

I had a similar problem. My problem was the resistor on the back of the unit was defective.

[extremesounds13]

Originally Posted by 70LonghornCST

I had a similar problem. My problem was the resistor on the back of the unit was defective.

By unit are you talking the gauge or the sending unit?

[70LonghornCST]

Sorry for the delay. I am refering to the back of the cluster. There is a little white rectangular resistor (attached to the rear of the fuel gauge) It is made out of fiberglass/fabric with thin coiled copper wires around it. Or, yours might be the other type: ceramic with metal inlaid copper connectors. They can go bad.

If that doesn't correct the problem, and you try all of the trouble shooting tips as mentioned above, it may be your fuel gauge itself.

[1971BB427]

This is all good info as my gauge isn't working either! Mine is stuck on full, and since I found broken wire at the right rear turn signal, I'm betting it's wiring at the elft turnsignal area where the harness goes through.
Some joker had trailer wiring on it and when he removed those displacement splices it broke the wiring. I'm guessing that's the same for the left side too.

[AzDon]

Single wire to the back is brown..... If it registers full, the wire is bare and touching ground somewhere or the float is stuck up (not likely) If it registers empty, the wire is broken or disconnected. The wire is unpluggable behind the gas tank.

[extremesounds13]

Originally Posted by AzDon

Single wire to the back is brown..... If it registers full, the wire is bare and touching ground somewhere or the float is stuck up (not likely) If it registers empty, the wire is broken or disconnected. The wire is unpluggable behind the gas tank.

So when I unplug the gauge from the fuse box and it goes to the three o clock position is it grounding out and that why it does that or is that what it is supposed to do when its unpluged?

[Longhorn Man]

it's supposed to do that when unplugged

[rockc]

I had the same problem with mine not reading correctly. Had to get the whole new sending unit from summit racing. They were the only ones that had a unit that was close to the original.

[doctrouble]

When i turn my ignition on it jumps right to the 3 o clock, but when its off, it slowly (over weeks) moves to maybe 12-1 o clock

[1971BB427]

Originally Posted by AzDon

Single wire to the back is brown..... If it registers full, the wire is bare and touching ground somewhere or the float is stuck up (not likely) If it registers empty, the wire is broken or disconnected. The wire is unpluggable behind the gas tank.

Ok I'm really confused now. Troubleshooting the wire from gauge to the tank and found several things.
1-With no power to the gauge (fuse pulled) the gauge reads full. Connect power and it goes to empty with a full tank of gas.
2-The wire at the tank doesn't go from the Pass. side, it goes through the driver's side rear tailight area.
3-When I pulled the wire the gauge goes to empty.
4-When I ground the wire the guage goes to full.

Read the sending unit with a full tank of gas and I get 8 ohms resistance to ground.
Not sure if the sending unit reads 90 ohms full or empty. Anyone know for sure?

[robertrocha6]

ok so my guage isnt working now...but there is a wire with a round tip on it just hanging....was this connected to the back of my fuel guage, my guage is reading full. i tested the tree pins on back and one registers 6 volts and the other 12 volts when the ignition is on. help!

1972 chevy c10

[AzDon]

Originally Posted by 1971BB427

Ok I'm really confused now. Troubleshooting the wire from gauge to the tank and found several things.
1-With no power to the gauge (fuse pulled) the gauge reads full. Connect power and it goes to empty with a full tank of gas.
2-The wire at the tank doesn't go from the Pass. side, it goes through the driver's side rear tailight area.
3-When I pulled the wire the gauge goes to empty.
4-When I ground the wire the guage goes to full.

Read the sending unit with a full tank of gas and I get 8 ohms resistance to ground.
Not sure if the sending unit reads 90 ohms full or empty. Anyone know for sure?

What I am saying is that with all the wiring hooked up and hot at the dash, you check the brown wire going to the sender where it unplugs behind the back bumper. Since the sender works as a varible grounding device, you should be able to produce "full" and "empty" readings by either disconnecting this wire or touching it to ground. There is also a ground-to-ground wire from the sender to the frame that must be connected properly for the sender to complete ground to the frame, but it is not involved in this test...

TANK WIRE GROUNDED=FULL TANK WIRE DISCONNECTED OR BROKEN=EMPTY

[AzDon]

With everything hooked and hot at the dash, If you can unplug the brown gauge wire behind the bumper and it goes empty and then, when you touch this wire to bare metal, it goes to full, This test result indicates that your gauge and wiring are working properly back to this point and your problem is the wire from the plug to sender, the sender itself, or the sender's grounding wire

[1971BB427]

Thanks guys! I guess my next step is to run the Burb enough to get the tank close to empty and drop it. Sounds like I've either got a bad sending unit, or a float that's sunk.
I had contemplated cutting the deck above the sending unit to make an access hole to work on the unit, but I think I'd ratherr not damage a perfect deck.

[extremesounds13]

Finally worked on mine again today and got it figured out. I dropped the tank and the float had sunk, it had all sorts of rust on it and had ate through it so it could never rise. So I grabbed a sending unit I had laying around from a 71 truck and the float part was the same so I installed it put everything back together and it works like a champ!! Thanks for all the advice guys.