Fuel gauge / Negative ground

[rjfoster03]

Have a "new" addition and the Healey is set up with a negative ground, but the Fuel Gauge reads "backwards" so empty on the gauge is a full tank and full on the gauge is actually empty in the tank.

Can the wiring on the fuel gauge be reversed to make the gauge reflect what is actually in the tank?

 

[Nelson]

That would do it.

 

[dklawson]

No. Neither the early gauge systems nor the late gauge system were polarity sensitive.

In all likelihood you have an early sender with a late gauge or vise-versa.

The early gauge systems worked with electromagnets and can easily be identified by the fact that their needles "jump" off of the rest peg as soon as the ignition is turned on. The needles also bounce around when you drive over bumps. Their sending units worked with decreasing resistance as the tank empties. That is to say, the sending unit has less resistance when "Empty" and more when the tank is "Full".

The later gauge systems require the voltage stabilizer. Their gauge needles move SLOWLY when you turn on. Their gauge needles may vibrate when you hit bumps while driving but they don't bounce. They work by resistance heating inside the gauge. The sending unit will have more resistance when empty and less resistance when full.

Because the two gauge systems use sending units with different ranges and change resistance in different "directions", you cannot mix the components.

Regularman (a.k.a. Kim Webb) is the Spridget gauge guy on this forum. He can walk you through how to test your gauges and calibrate them.

BTW, where in NC are you?

 

[rjfoster03]

Thanks for the information. I will try and locate Regularman on the forum.

I am in the Greensboro area.

 

[regularman]

Thanks for the information. I will try and locate Regularman on the forum.

I am in the Greensboro area.

Hey, you any good with a soldering Iron and working with things that you hope you don't break? You could take apart the sender and inside there is a slider that goes up and down a wire wound resistor(WWR). One end of the WWR is gounded and the other end is open. As the slider moves up and down the WWR the resistance (to ground) changes.
What you need to do is ground the other end of the resistor and open up the grounded end. Some of the senders just have the end of the WWR that is grounded just pinched in the cover on that end and you could just pull out the WWR spool and spin it around and you would have it.
They swapped these things in the way that they work at some point due to the fact that on the old style if the wire from the tank to the gauge opened up, it would read full all the time and its better for it to read empty with a broken wire instead.
Also you need to see what kind of gauge you have. The older kind worked on 12vdc, the later kind had the voltage stabilizer that worked on 10vdc. The stabilizer was to keep the voltage to the gauge constant, with the 12v earlier types, the gauge might read differently when stopped at a light with the heater fan, headlights, etc on and the old Gen not putting out enough to keep the system at 12v.
Let me know if I can help.

 

[dklawson]

Kim, are the early and late sender resistance ratings close enough that you can simply change the ground connection? I thought the early senders read (about) 10-90 empty-to-full, and that the later gauges read (about) 270-30 empty-to-full.

If you do decide try reversing the windings, I remember that the resistance wires are a little difficult to "tin". You will need to really clean the end of the wire and probably use acid flux. Be sure to neutralize any acid flux with sudsy ammonia and rinsing with water before putting the sender back in service.

 

[regularman]

Kim, are the early and late sender resistance ratings close enough that you can simply change the ground connection? I thought the early senders read (about) 10-90 empty-to-full, and that the later gauges read (about) 270-30 empty-to-full.

If you do decide try reversing the windings, I remember that the resistance wires are a little difficult to "tin". You will need to really clean the end of the wire and probably use acid flux. Be sure to neutralize any acid flux with sudsy ammonia and rinsing with water before putting the sender back in service.

All of them start at 0 ohms (but you might read 10 or so at the gauge going though some wiring resistance or something). The wiper hits the end of the wire resistor and makes more or less a dead short to ground. Most of the early ones were 0 ohms and 70 ohms, then the later ones were 0 and around 270 I think is right. I don't think I have dealt with a 90 ohm one, that is one lots of US types but then the rubber bumper cars might be different, I haven't played with one of those. I have found the replacement senders to be pretty far off the mark and have had to calibrate a couple of them by removing windings. They were so far off I could not make up for it with gauge calibration, so I had to change it. Another one was high and I didn't like the way it looked inside (cheap and easy to break)so I put another resistor in parallel with it to get the resistance right.

 

[regularman]

Kim, are the early and late sender resistance ratings close enough that you can simply change the ground connection? I thought the early senders read (about) 10-90 empty-to-full, and that the later gauges read (about) 270-30 empty-to-full.

If you do decide try reversing the windings, I remember that the resistance wires are a little difficult to "tin". You will need to really clean the end of the wire and probably use acid flux. Be sure to neutralize any acid flux with sudsy ammonia and rinsing with water before putting the sender back in service.

Some of them are downright impossible to tin. I was a certified solderer in the Air Force and tried every trick I know and could not get it to bite at all on one of them. In that case put some super glue or something on the end of the tube and leave enough of that wire sticking out to bend around one of the cover screws and tighten it in there is the best I could do. It was originally placed around the end of the tube and the tube being pressed in held the wire against the case for a connection. I didn't like that at all.
Again though, the only way to get a fairly accurate gauge is to calibrate the gauge with the sender, there is variability in all of them. I got mine set for having about 1.5 gallons left when it reaches empty. I usually fill up when it reads 1/4 tank and it takes 4 gallons.

 

[dklawson]

Thanks Kim. I'm still a bit curious about the resistance range for the later Spridget bimetallic gauges. I think BMC/BL standardized on the 30-270 (full to empty) range once the stabilizer was introduced. On cars built before the stabilizer was introduced I've seen resistance ranges all over the place but all decreased from full to empty.

 

[regularman]

Thanks Kim. I'm still a bit curious about the resistance range for the later Spridget bimetallic gauges. I think BMC/BL standardized on the 30-270 (full to empty) range once the stabilizer was introduced. On cars built before the stabilizer was introduced I've seen resistance ranges all over the place but all decreased from full to empty.

I have never read 30 but that might be true for some. Mine has the stabilizer but the sender did not read 30 ohms, but its a 71. I am not sure, to be honest. There could be several different ones that I have not seen from smiths. Its cold weather now and not good riding weather for open top cars. Maybe Rick can remove the sender and gauge and get them to me and they can be sorted out. If its a Healey and - ground then its got to be before the stabilizer, but he might have a sender out of something different in there. I would think his setup would be the same as the bugeye.