Vintage 140 fuel gauge reading low (not the usual suspects)

After years of not having one I finally took it upon myself to get a GT cluster with a working fuel gauge. I plugged it in to confirm all the gauges and lights functioned and I noticed that the fuel gauge read a lot low (like only comes up to touch the redzone), but wasn't sure exactly how much fuel I had in the tank. So I filled it up but unfortunately it didn't change the reading on the gauge.

NOTE: It is JUST the fuel gauge. The Temp gauge reads normal, dead in the middle.

Following that I took these steps:

• I took it to a speedometer shop to have the odometer gear replaced and the tach calibrated, and generally cleaned up, and still the fuel gauge doesn't work.
• I checked the ohm reading with a full tank, and it's reading 10 ohm as the 1968 greenbook says it should.
• I grounded the wire to the sender body to confirm the gauge does the full sweep (I only did it briefly).
• I swapped out 3 or 4 known working voltage regulators to see if that was the problem maybe.
• Even though the fuel sender itself is only 3 years old, I tried my old sender just in case and it got the same reading.

At this point I'm not sure what could cause the fuel gauge alone to read low.
Any suggestions would be very helpful.

Check the wire for the gauge from the tank to the dash, could be resistance throwing off your reading?

283SD said:

Check the wire for the gauge from the tank to the dash, could be resistance throwing off your reading?

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Check the wire for what though? What would the resistance in a wire look like?

oemoilleaks said:

Check the wire for what though? What would the resistance in a wire look like?

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If is 12v at the dash it should be 12v at the tank.

283SD said:

If is 12v at the dash it should be 12v at the tank.

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That makes sense... but this is a 5v cluster. I'll look for the right voltage

Do a little bit of checking.

http://forums.turbobricks.com/showpost.php?p=5018874&postcount=1

Some of the R sport clusters had different senders. I don't know whether this applied to the fuel sender on your particular cluster. Hiperfauto could probably give you the straight scoop.

Is it a GT or a Rallye, how many dials. Has yours got oil pressure, if so it?s a Rallye. The Rallye use a different sender.

mitch1971 said:

Is it a GT or a Rallye, how many dials. Has yours got oil pressure, if so it?s a Rallye. The Rallye use a different sender.

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it's a GT cluster for sure. 4 gauges. Meaning the senders are the same as the stock cluster.

Today it started at the 0 mark and then just slowly disappeared.