Fuel Guage Ohm Range?

[66 Red Rocket]

I am planning on putting auto meter guages in my 66 bb coupe this winter, but have no idea what the ohm range on the fuel level sender is. I need to know empty to full. Thanks a bunch , John

 

[Vetsvette2002]

I am planning on putting auto meter guages in my 66 bb coupe this winter, but have no idea what the ohm range on the fuel level sender is. I need to know empty to full. Thanks a bunch , John

Should be from 0 to 90 give or take a few ohms
Don

 

[Geek's 65]

Trick question. Depends on how you measure it. These are not the standard ole resistance provides the fuel level systems. This is a three wire (12VDC on one of them) voltage driven system. If you disconnect the wires from the sender and read between the pins where the black with purple stripe wire (this is the one with 12VDC) and the tan wire were, then empty is 0 ohms and full in 90 ohms. If you read between pin where the the tan wire was (tan wire goes to the guage) and ground, then empty is 90 ohm and full is 0 ohms. If you leave the wires connected and try to read the resistance, you get the gauge and a few other odds and ends in there to mess up the measurement.

 

[JohnZ]

I believe the AutoMeter gauge is designed for an industry-standard 2-wire resistance-only sender (I know they were when I installed them in my Grand Sport with a fuel cell and standard 2-wire 0-90 ohm fuel cell sending unit). The '63-'67 Corvette is the only GM car (other than mid-60's Cadillacs) that ever used a powered 3-wire voltage-divided sender and gauge.

The AutoMeter gauge MAY work if you disconnect the 12V feed to the stock sending unit so all the gauge is reading is the tan wire (resistance through the tap to the variable resistor to ground), but I'd want to bread-board it first.

Here's the C1/C3 (and AutoMeter/industry standard) 2-wire resistance-only system:

Here's the '63-'67 3-wire powered voltage-divider system:

 

[00fxd]

Does anyone know what if any benifit was to the complicated 3 wire sender system? A thought for red rockets conversion might be to use a later Corvette 2 wire sender. Should fit right into the bung.

 

[66 Red Rocket]

Thanks Guys

Thanks So Much To All And Especialy Johnz For The Wireing Digram. I Have A Question For Johnz. What Is "bread-board", I Am Totaly Unfamiliar With That Term?

 

[BarryK]

66, I'm not John and don't wish to interfer with his answering your question but i believe he means to mock-up the parts and the whole circut on the bench first to make sure it's working correctly before you go and make changes to the wiring in the car itself. You should be able to do that with a battery, the AutoMeter gauge, and the sender unit laid out and wired up as he stated above on your bench and than test the whole thing for proper operation. This way if it works than great, if it doesn't, you will know that before you cut any of the cars wiring harnesses to make the stock 3-wire system work with the 2-wire AutoMeter guage.

 

[67HEAVEN]

Barry has it right.

Here's something to help make it clear...
http://www.iguanalabs.com/breadboard.htm

With some basic materials, you can make one for yourself.

 

[BarryK]

Barry has it right.

WOW!! let's all write this date down as it doesn't happen very often......

 

[Ken Anderson]

You can use a 68-74 fuel meter/sender with any 90 ohm gauge. The correct fuel meter/sender used in 63-67 Corvettes will not read correctly with a 90 ohm gauge. The midyear sender was reworked/revised in 66 to correct the dash fuel gauge reading too low with a full tank of gas.

 

[Ron Miller]

You can hook up an connect JohnZ's circuit to test yours a lot quicker and cheaper with a few jumper wires and a 12 volt battery on your bench, don't need a full blown bread board. Just go by his wiring diagram.

 

[Bolisk]

I know this is an old thread. . .but I'm having fuel gauge issues as well.

Does anyone know what is the correct ohm resistor for the back of a 1970 Fuel Gauge?

I'm referring to the little resistor thingy the bridges the to posts on the back of the fuel gauge.

My 1970 corvette had a later model fuel gauge in it. . .I think a 77 or something. It was the gauge that had white letters, and the powder blue paint on the back. It worked perfectly fine (100%) correct with the replacement sending unit that I installed.

I replaced that fuel gauge with a re-manufactured correct fuel gauge. . .and I reused the resistor that was on the back of the wrong old fuel gauge.

Now when the tank is "FULL", the gauge read 1/4 full. When the tank is "EMPTY", the gauge reads empty.

I'm thinking I have the wrong resistor on the back of the new gauge. . .but I'm not sure why it's there in the first place as all sending units for C3's are 0-90 ohm's. So whats the point of the resistor on the back of the gauge, and WHY in the name of all things holey does no wiring diagram show the resistor?!?!?

Any other ideas or advice is would be helpful.

Thanks
Jon