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Old 06-19-2019, 02:09 PM   #1
chevyfiftynine
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Join Date: Mar 2010
Location: Glasgow, UK
Posts: 16
How is fuel gauge wired?

I have a 58 Chevy Apache 235. The fuel gauge used to work, started flickering for a while, then stopped. I got a new sender, then I did a partial re-wire but it still doesn't work. It would help to understand how it works in the first place. From the centre terminal on the sender there is a black wire which is connected to a white wire which goes into the loom under the truck. The white wire on the sender is secured to a fixing screw on the top of the sender, and the wire disappears behind the tank. I've renewed the black section. Is the white from the sender earthed under the tank, and where does the lead go from the terminal after going into the loom? I'd heard that the sender is wired so that no live supply goes into the tank. If the white from the sender is earthed, where does the positive feed come from? Any ideas?
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Old 06-19-2019, 02:32 PM   #2
mongocanfly
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Re: How is fuel gauge wired?

all the sender is is a varible resistor ground...
this may help explain it better....https://auto.howstuffworks.com/fuel-gauge1.htm
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Old 06-23-2019, 09:56 AM   #3
Dead Parrot
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Re: How is fuel gauge wired?

Found this site that references older GM gas gauges:https://www.fillingstation.com/artic...ugetesting.htm

Newer ones, 60's until they went digital work the same but the ohms changed to 90. If your sender is 90 ohm but your gauge is expecting 30, the needle should move a little but won't do a full scale reading.

Simple description is one wire from gauge to sender and a second wire from body of sender to ground. Not sure when GM added the sender to frame grounds. Earlier years may have assumed the tank mounting system provided a ground.

General rules:
Never connect live power to sender wiring.
Max full all the time is open circuit/missing ground on sender wiring.
Empty all the time, short circuit in gauge to tank wiring.
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Old 06-23-2019, 12:55 PM   #4
chevyfiftynine
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Join Date: Mar 2010
Location: Glasgow, UK
Posts: 16
Re: How is fuel gauge wired?

Thanks Mongo and Dead Parrot for the useful links. What I haven't done yet is to look under the dash to check if the connections to the gauge are faulty. I assume that when the wire from the sender goes into the loom under the truck it comes out at the gauge. It's unlikely the wire is broken inside the loom, so it's looking like the fault is with the gauge or connections to it. I'll look at it this week and let you know.
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