72 Fuel Gauge
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8th Gear
Joined: Mar 2010
Posts: 8
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72 Fuel Gauge
I am having some issues with a fuel gauge and I am at a dead end. Initial diagnoses was a bad sending unit, heavily corroded and no ground. Got a new one from Corvette America. Out of the box the new sending unit bench tested at 4 ohms empty and 96 ohms at full. I hooked only the wires to it so I could manipulate the float. the gauge would read empty but would stop at 1/2 tank. Following Willcox's troubleshooting guide I removed the signal wire from the sending unit and it stopped at 1/2 tank. Then grounded the signal wire and it read empty on the gauge. So I moved to the pigtail connector in the driver side kick panel area. Was still getting an ohm reading so moved to the gauge. Tested the resistor strip on the back out of the car. It read at 89.4 ohms. I replaced the gauge with a new one from Corvette America.Starting over essentially. With the new sending unit hooked up gauge will read empty and roughly 4 O'clock position in full. Removing the signal wire from the sending it pegs to the 3-4 o'clock and grounded out moves to empty. Now when the sending unit is hooked up it reads empty but when I manipulate it to anywhere more than a 1/4 tank it pegs to 4 o'clock. I retested the sending unit unhooked and it sill reads 4 ohms empty and 96 full, however, when it is hooked to the car I am getting a 30 ohm reading on my multimeter at empty (gauge reads empty) at full for some reason getting like 140ish ohms. i have even ran a new test wire from the sending unit straight to the gauge and a new ground to be on the safe side with same results. I have retested the sending unit several times off the car and still get 4 ohms empty and 96 full, but when hooked to the car the gauge reads empty and anything more than a 1/4 of a tank pegs to 4 o'clock.Any thoughts? Would be greatly appreciated!Did some more testing. I have another 69 Vette in the shop that I hooked the wires to this new sending unit. Gauge responds as it should. Full stops at full etc...So the issue appears to be wiring in the car.... The Pink wire going to the back of the gauge is getting 12v with key on. Housing is grounded. According to the Willcox walkthrough of testing this new gauge I put in responds as it should.... it just doesnt when the sending unit is attached?
Last edited by CorvetteRestoration; Apr 19, 2019 at 01:27 PM. Reason: Updates
Thread Starter
8th Gear
Joined: Mar 2010
Posts: 8
Likes: 0
Update** Upon further testing and speaking with a vendor. The new AC Delco gauges apparently do not require the use of the OE resistor on the back of the gauge. Removed the resistor and retested the gauge. All is working as it should with correct ohm readings.
One would think they would include such a note with that $80 gauge.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
They all come with instructions.... they are just so tiny that they are hard to read. I posted an enlarged copy on my tech site which makes... for me easier reading. But in the bottom of each gauge is this tiny folded up piece of paper and it's very common for customers to not ready it (and I can see why) before installing.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Update** Upon further testing and speaking with a vendor. The new AC Delco gauges apparently do not require the use of the OE resistor on the back of the gauge. Removed the resistor and retested the gauge. All is working as it should with correct ohm readings.
Willcox
Thread Starter
8th Gear
Joined: Mar 2010
Posts: 8
Likes: 0
They are not new AC Delco gauges... unfortunately they are imported in an AC Delco box. All the imported gauges don't use the resistor because the resistance is built into the gauges. This is why you can't use our adjustable temperature resistor on an imported reproduction dash unit.
Willcox
Willcox
