Fuel gauge working opposite

[2001convertable]

Hi, I installed the fuel tank back in the cab today. I took the wire off the rear tank last week and ran it into the cab for the relocation back into the cab. I figured that I would check the sending unit with my multimeter on resistance.With the leads red on sender terminal and black onto housing. As I raised the float to full max the meter read 30 ohms which is good. I grounded the wire to the old tank that I routed back into the cab and the gauge went from empty to full.I then took the sender unit and attached the fuel gauge wire to the connector on the sender and grounded the housing. With the float down the gauge read full. When I raised the float it went to empty. The sender was grounded as well. This is working oppositely. I was wondering that the rear tank install from previous owner was wired for that tank and there would be some type of resistor of capacitor or something or maybe the gauge has the opposite polarity. I also felt a little electric charge as I was holding the sending unit.I took a voltage reading at the hot wire going to the sender and it read 7.42 volts. I read the battery in the truck and it read 12 volts.If someone has an idea please help....thank you

[mongocanfly]

I don't think you should have any voltage at the sending unit..that should be a ground wire going to the sendeing unit i think....the sender completes a ground cicuit and the resistance is what the gauge sees..I may be wrong on this.....

[2001convertable]

Hi, its strange because that was the same wire that was on the rear tank sender. It saves to be working but opposite. I did a google search and found that someone said to reverse the wires on the gauge.

[mongocanfly]

this may help some.....
http://67-72chevytrucks.com/vboard/s...d.php?t=640615

[Jesse Z]

Obviously your tank is upside down. Turn it over and the sender should be oriented properly.

I'll go now...

[2001convertable]

That's very funny it gave me a good laugh...

[GreasyLikeaBurger]

Originally Posted by 2001convertable

Hi, I installed the fuel tank back in the cab today. I took the wire off the rear tank last week and ran it into the cab for the relocation back into the cab. I figured that I would check the sending unit with my multimeter on resistance.With the leads red on sender terminal and black onto housing. As I raised the float to full max the meter read 30 ohms which is good. I grounded the wire to the old tank that I routed back into the cab and the gauge went from empty to full.I then took the sender unit and attached the fuel gauge wire to the connector on the sender and grounded the housing. With the float down the gauge read full. When I raised the float it went to empty. The sender was grounded as well. This is working oppositely. I was wondering that the rear tank install from previous owner was wired for that tank and there would be some type of resistor of capacitor or something or maybe the gauge has the opposite polarity. I also felt a little electric charge as I was holding the sending unit.I took a voltage reading at the hot wire going to the sender and it read 7.42 volts. I read the battery in the truck and it read 12 volts.If someone has an idea please help....thank you

First I assume this is a stock tank with a stock sender for a '59? So the stock gauge should be a 0-30 ohm sender. sounds like the sender is working properly when you bench tested it.

You noted that there was voltage on the sensor wire, there should be no voltage on that wire. It is for a resistance reading only, you might have a wiring issue between the sensor and your fuel gauge.

Pics would help too.

[1project2many]

This is an interesting question to me. 55+ passenger cars are three wire gauges. On these gauges you can swap two wires (power and ground) and the gauge will operate in reverse. But the truck gauge is a two wire gauge which, I *believe*, grounds through the body of the gauge and cluster. Swapping wires IIRC lets out the magic smoke. I have an old cluster in the barn and I will try to get out there to do some testing.

http://www.adlersantiqueautos.com/ar...ntcluster.html

You noted that there was voltage on the sensor wire, there should be no voltage on that wire. It is for a resistance reading only, you might have a wiring issue between the sensor and your fuel gauge.

Oh, this could be right in some situations. We're talking key on, so there has to be current available from the gauge. The reading on the voltmeter will depend on where the current is allowed to go.

Key on, wire from gauge disconnected = full voltage. Current cannot go to ground, voltmeter reads full potential.

Key on, wire connected to sender, sender not grounded = full voltage. Current still cannot go to ground so voltmeter reads full potential.

Key on, wire connected to sender, sender grounded, float arm all the way up = partial voltage. Most current can get to ground through 30 Ohm resistance.

Key on, wire connected to sender, sender grounded, float arm all the way down = no voltage. All current can get to ground.

The "full potential" number will depend on the type of gauge.

[2001convertable]

Thank, I have an extra cluster and tomorrow Im going to bench test it. I think the polarity is wrong.I have to fire out how to take out the cluster from the dash.

[NeoJuice]

I had a similar problem that when I turned my ignition 'on' my fuel gauge would go to full. There is one wire that went from my autometre gauge to the fuel sending unit and no ground wire. I had to add a ground wire from one of the sending unit bolts and mounted it to body on clean sheet metal. Here is a helpful link I used for troubleshooting.

https://www.fillingstation.com/artic...ugetesting.htm

[tmoble]

reverse the wires on the gauge.