Mercury Cougar, 1985 - Fuel Gauge reads wrong

I own a 1985 Mercury Cougar.
My fuel gauge functions, but always shows far less than it should (top 20-25L at best?).
Suggestions?
Do I need to replace/adjust the float, or might it be more?
What should I check? Can I adjust/change the float without dropping the tank on this (any) model?
snipped-for-privacy@telus.net
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I had an 85 T-Bird which is pretty much the same car as your Cougar. If you live in an area where the road crews use salt in the winter expect the top of the gas tank to rust and perforate. DO you smell any gas when you fill it up ? The fuel pump filter assembly is held in the top of the tank by a ring that gets very rusty. Once you take an original pump out expect to replace the entire assembly including a new locking ring and maybe a new tank as well. Accurate fuel gauge readings are hampered by poor electrical grounds and the use of a marginally working voltage regulator attached to the back of the instrument cluster. As these cheap regulators age they don't provide the proper voltage to the gauges (think it was 7.5 volts) causing all kinds of misleading things to happen to the analog gauges. You won't see this if you have the full digital dash. The cluster is a real pain to take out from what I remember. In 230,000 miles I had the cluster out at least three times for replacing the halogen lamps for the LCD speedo display and once removed the entire dash to replace the heater core. One of the ugliest jobs I've ever attacked.
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No more than is usual (any vehicle, any time) when near the pump during fill and nozzle extraction.
There is no obvious evidence of leaking. My fuel consumption is quite low (for my limited experience). A full tank lasts more than 400km, driving back and forth to work (10-15mins, 50-60kph) every weekday, and toodling around town the rest of the time.

kinds of misleading

full digital

I have partial digital. The fuel gauge is an analogue needle.

miles I had

the LCD speedo

of the ugliest

Ouch... I hope I won't have to do that for a while! (at least until I have to restore it)
Thank for your time Steve. I'll definitley probe a little deeper.
Wolfman
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