Aftermarket fuel gauge reads either full/empty. 2 prong sender unit.

[Milesdodge]

Hi all,
I’ve fitted an aftermarket fuel gauge (recommended elsewhere on FABO) which is the correct ohm range.
I went to check the sender unit connections and was suprised to see two prongs. I earthed the strap and connect sender wire to prong 1
Gauge goes to below empty
Connected sender to prong 2
Opposite reaction, gauge reads full!
Can anyone provide me with a steer on what’s happening here, please.

 

[BeepBeepRR]

In the picture you posted. The ground strap from the sender is supposed to clip onto the metal line before and after the rubber. You do not have it grounded without that strap.

 

[Milesdodge]

In the picture you posted. The ground strap from the sender is supposed to clip onto the metal line before and after the rubber. You do not have it grounded without that strap.
View attachment 1244155View attachment 1244157

Sure, the pic was taken before I started work on it. The ground strap is now earthed to the chassis.

 

[BeepBeepRR]

Sure, the pic was taken before I started work on it. The ground strap is now earthed to the chassis.

Ok. Wasn't sure by the picture. I have an issue with the Roadrunner fuel sender too. I pulled it back out and checked it with an ohm meter and also pulled it out and hooked it up directly at the kick panel plug that goes to the back of the car. I think my issue is in the wire going to the trunk. because when I tested it at the plug and went from empty to full the gauge worked good. When I hooked it back up at the tank with the OE wire it reads messed up. Never goes over half tank. There must be an issue with the wiring going into the trunk. You may have something else going on.

 

[dadsbee]

"Correct Ohm Range"... which would be about 10 to 72 ohms, BUT is it in the correct direction??? 10 ohms is when the tank is full, 72 empty. If it's assembled in the opposite direction then it's going to have the gauge working backwards.

I'd suspect if this none factory style gauge sender has two prongs then the sender rheostat is isolated from the assembly and you need to be using both prongs. One would be ground, the other hooked to the gauge wire. If both are insulated from the assembly/casing then which pin goes where doesn't matter.

Put an ohm meter on it so you know what you are dealing with. One prong may be there for ease of use, but also be grounded to the assembly and the other prong would be the "output" to the gauge wire.

 

[slickrick]

You have to pull the sender and "bench test" it with the original wiring and grounded to the fuel line. If it is not working, your wiring is somewhere shot or your fuel line is not grounded.
So ground the fuel sender with an extra wire and check again.
You should also ground the gauge to see if the needle is moving the complete way. But only for a short time. Do not destroy your gauge.

If nothing helps you can try the "Fuel Bridge" from Autometer or the "MeterMatch" from Tanks. With this devices you can nearly calibrate every sender with every gauge. Pretty Cool!!

Cheers
Flo

 

[Milesdodge]

"Correct Ohm Range"... which would be about 10 to 72 ohms, BUT is it in the correct direction??? 10 ohms is when the tank is full, 72 empty. If it's assembled in the opposite direction then it's going to have the gauge working backwards.

I'd suspect if this none factory style gauge has two prongs then the sender rheostat is isolated from the assembly and you need to be using both prongs. One would be ground, the other hooked to the gauge wire. If both are insulated from the assembly/casing then which pin goes where doesn't matter.

Put an ohm meter on it so you know what you are dealing with. One prong may be there for ease of use, but also be grounded to the assembly and the other prong would be the "output" to the gauge wire.

Thanks, the gauge itself has just the one connection for the sender to tank line; it’s the sender unit itself that has two ‘live’ (?) prongs. They can just be seen in the pic I posted, somewhat shaded.

 

[Milesdodge]

You have to pull the sender and "bench test" it with the original wiring and grounded to the fuel line. If it is not working, your wiring is somewhere shot or your fuel line is not grounded.
So ground the fuel sender with an extra wire and check again.
You should also ground the gauge to see if the needle is moving the complete way. But only for a short time. Do not destroy your gauge.

If nothing helps you can try the "Fuel Bridge" from Autometer or the "MeterMatch" from Tanks. With this devices you can nearly calibrate every sender with every gauge. Pretty Cool!!

Cheers
Flo

Thanks Flo. The gauge is definitely grounded. What is throwing me out is the the ga t that the sender u it at the tank has two prongs. Depending on which I connect I get opposite results. Either full or empty.
Yes, the meter match does look useful.

 

[dadsbee]

Thanks, the gauge itself has just the one connection for the sender to tank line; it’s the sender unit itself that has two ‘live’ (?) prongs. They can just be seen in the pic I posted, somewhat shaded.

Sorry, I meant to type none factory SENDER.. not gauge... and it everything else applies..

 

[Milesdodge]

Ok thanks hanks for all the advice. Looks as if my two prong sender unit needs one prong to earth, hence the results I got when applying the blue wire. I’m going to earth one and have the other to the gauge. Hoping that sorts it out.