Gas Gauge Voltage - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Doug66 · 12-02-2018, 08:34 PM

I'm debugging a fuel gauge error and found the voltage at the stock fuse panel spade terminal for "Gas Gauge" is only 7.8 volts. My tank resistance on a 30 ohm sending unit is correct at the current fill level: 26.7 ohms at 3/4 full. However, I cannot get an empty gauge reading grounding the sending unit wire. It will go to max gauge reading disconnected and key on however.
The 7.8 volts is puzzling. Should it be 12+ volts?
Thanks for all the help!

**PGSigns** · 12-02-2018, 09:30 PM

The low voltage is either a bad ground or a corroded terminal driving the resistance up causing the voltage drop.
Jimmy

Doug66 · 12-03-2018, 09:36 AM

Is the resistor pad across the positive and sending wire terminals common on early gauges giving me the 7.8 volts possibly? I pulled the fuse next to the terminal, cleaned/sanded the posts and installed a new fuse with dielectric grease to ensure a good connection. While the fuse was out, I checked the voltage at the spade and, again, 7.8 volts. Total frustration.
Thanks again for the help.
Doug

**TBONE1964** · 12-19-2018, 10:16 PM

So you have a fuel gauge that has power, ground and a signal wire.

The power wire is the pink one and should have battery voltage with the key on. The signal wire will show voltage and that voltage will be resisted voltage from the sending unit depending on how much fuel is in the tank.

If you had the sending unit out of the tank and moved the float, it should change the voltage on the signal wire, which is the tan one. The ground comes through the cluster itself.

Can you tell me what the actual issue is?

Hope this helps,
Tom

Doug66 · 12-20-2018, 05:19 AM

I had replaced the original gauge with "Shanghai Junk" and could not get the gauge to "0" reading when grounding the panel wire. Sent the original gauge to Williamson's for repair and all is good now.

Had a "Shanghai Junk" repop tach same issue. Williamson got it working. Shame on me for twice buying off-shore. We have no choice sometimes but to add to our landfills.

Thank you for the reply and Merry Christmas
Doug

andyh1956 · 12-23-2018, 01:39 AM

Doug who is "Williamson's"?
Thanks

Doug66 · 12-23-2018, 05:23 AM

Williamson's Instruments in Chester, Arkansas. Great people.

12-02-2018, 08:34 PM	#1
Doug66 Registered User Join Date: Oct 2015 Location: Ocala, FL Posts: 18	Gas Gauge Voltage I'm debugging a fuel gauge error and found the voltage at the stock fuse panel spade terminal for "Gas Gauge" is only 7.8 volts. My tank resistance on a 30 ohm sending unit is correct at the current fill level: 26.7 ohms at 3/4 full. However, I cannot get an empty gauge reading grounding the sending unit wire. It will go to max gauge reading disconnected and key on however. The 7.8 volts is puzzling. Should it be 12+ volts? Thanks for all the help!

12-02-2018, 09:30 PM	#2
PGSigns Senior Member Join Date: Jan 2011 Location: Hayes Va Posts: 4,569	Re: Gas Gauge Voltage The low voltage is either a bad ground or a corroded terminal driving the resistance up causing the voltage drop. Jimmy __________________ 60 to 66 Chevy and GMC window decals http://67-72chevytrucks.com/vboard/s...d.php?t=661131 Good friends, good food and a hotrod what else do you need? 1966 BBW long fleet Daily driver 1965 BBW short fleet Sold and going to a good home 1965 Suburban 2003 3500 Duramax 2005 Ultra Classic

12-03-2018, 09:36 AM	#3
Doug66 Registered User Join Date: Oct 2015 Location: Ocala, FL Posts: 18	Re: Gas Gauge Voltage Is the resistor pad across the positive and sending wire terminals common on early gauges giving me the 7.8 volts possibly? I pulled the fuse next to the terminal, cleaned/sanded the posts and installed a new fuse with dielectric grease to ensure a good connection. While the fuse was out, I checked the voltage at the spade and, again, 7.8 volts. Total frustration. Thanks again for the help. Doug

12-19-2018, 10:16 PM	#4
TBONE1964 Cluster King Join Date: Nov 2012 Location: Junction City, OR Posts: 5,263	Re: Gas Gauge Voltage So you have a fuel gauge that has power, ground and a signal wire. The power wire is the pink one and should have battery voltage with the key on. The signal wire will show voltage and that voltage will be resisted voltage from the sending unit depending on how much fuel is in the tank. If you had the sending unit out of the tank and moved the float, it should change the voltage on the signal wire, which is the tan one. The ground comes through the cluster itself. Can you tell me what the actual issue is? Hope this helps, Tom __________________ Contact me on all of your gauge cluster needs. I specialize in restoration, repair and parts sales for 67-72 Chevy and GMC trucks. email me at tbonegarris@yahoo.com I am also a dealer for Counterpart for gauge cluster parts only. Also see my facebook page, CG&C

12-20-2018, 05:19 AM	#5
Doug66 Registered User Join Date: Oct 2015 Location: Ocala, FL Posts: 18	Re: Gas Gauge Voltage I had replaced the original gauge with "Shanghai Junk" and could not get the gauge to "0" reading when grounding the panel wire. Sent the original gauge to Williamson's for repair and all is good now. Had a "Shanghai Junk" repop tach same issue. Williamson got it working. Shame on me for twice buying off-shore. We have no choice sometimes but to add to our landfills. Thank you for the reply and Merry Christmas Doug

12-23-2018, 01:39 AM	#6
andyh1956 Registered User Join Date: Mar 2010 Location: thomastown mississippi Posts: 1,261	Re: Gas Gauge Voltage Doug who is "Williamson's"? Thanks

12-23-2018, 05:23 AM	#7
Doug66 Registered User Join Date: Oct 2015 Location: Ocala, FL Posts: 18	Re: Gas Gauge Voltage Williamson's Instruments in Chester, Arkansas. Great people.



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