The Stovebolt Site Forums The Shop Area The Electrical Bay One more gas gauge question

I have followed the gas gauge posts here a lot. so did as much as I could with mine before I got stumped. Pulled the sensor from the tank and the resistance wire had come unraveled. That got replaced. Checked the ground and it was good. new sensor reads 30 Ohms empty and 1.2 Ohms full nice smooth change all the way. Put my meter on the wire at the gauge and got the same readings so the wire from the tank to the gauge is good. Turn the key on and I get 12 V at the gauge on the other post. No movement from the gauge. Yes I am 12 volts. Reversed the wires on the gauge just for a test, gauge reads backwards. It tries to go past empty. Still no movement towards full even with the sensor at 1.2 Ohms. Is my gauge the issue? No rubbing on the bezel and not stuck. Oh yeah, 52 half ton.

Are you using a 12 volt gauge or original 6 volt.

Where did you get your sender from?
The gauge is set up to read 30 ohm full

Original gauge. Sender from Classic. Sender should read 30 Ohms at full? S#$% that ain't good. Will there be an issue with the voltage on the old gauge? I did the same conversion back in the day (1972) and don't recall ever worrying about the gauge. But who does at 22? Changed the Gen, regulator and lights. That was about all there was to it back then. Oh yeah a battery. No turn signals so no flashers. I did put a ballast resistor in line with the fan motor and was done. I will pull the sender out tomorrow. Just take the seat back off and undo the screws. Maybe I can reverse the sender to show 30 at full, maybe....There goes another day with this old truck

the sender works the way it works, there's no 'reversing' it ... some here say a 6V gauge will be fine on 12V, but it's recommended that a dropping ["runtz"] resistor be used, so yes, you may have fried the gauge using 12V

Bill

Not to be combative but the gauge tried to move when I reversed the inputs. What value is a "runtz" resistor? Is this to reduce the voltage at the gauge? Maybe limit the current through the gauge? Thanks for the help even if it is not what I want to hear.

Runtz style voltage reducer - it is a one-way reducer (input and output side on the reducer). Also, placing it incorrectly on the output side lets full voltage go through the fuel gauge (which, as Bill posted, could mess up the fuel gauge).

Fuel gauge Trouble Shooting from the moderator's website

12v to 6v gas/fuel gauge voltage reducer

Originally there was a red warning tag on the back of the gauge sender post. Warning not to apply power to the sender post

...pic...

Thanks to tclederman and DADS50 for the help. Love the website and got some good from it. Never aw that tag before, Thanks again

Why 1.2 Ohms when tank is full....Cause the metal float exploded in the tank. Instant submarine. How does a metal float blow up? Note to little Chinese guy that makes the float...No pressure required to make float float. Translate that! So now I have to find a float and still have to check the gauge. Ah well I could be inna bar looking.. never mind I will be OK.

Thanks Tim for the tip on 5th ave auto parts. Good tech info. Steve

Hi all,
So after reading a lot of comments on gas gauge tech, I've come to the conclusion that my original 6V gas gauge is no good. I've never seen it work before since I took the original gas tank out a while back(never used it) and have recently installed a new tank/sender. My truck HAS been converted to 12V and I did use a 12V to 6V reducer from ClassicParts.com. My multi-meter is reading 7-8 ohms at the sending unit and gas gauge terminal with about 4-5 gallons in a 16-17 gallon tank. The gauge needle does nothing with the key on/off and remains at empty. I did however notice that when the terminal wires are switched, that the needle jumps to full, but this would be wired opposite to how it should be(power going to the sending unit side). Is this typical for a gauge to read full with power going to the wrong terminal?
Thanks

Typically, it blows the gauge.

I have a spare gas gauge, but haven't been able to test it yet. The needle moves freely when tilting the gauge up and down. Hopefully I'll find out soon if it's any good. Anyone have recommendations on a 12V replacement gas gauge?
Thanks

Nice !! I was just about to post a new topic to verify the hook up on the back of my gauge and thought I should do a topic search first. Your picture hit the spot as I have remnants of that red tag. Thanks!!