A 1965 Barracuda had the voltage limiter inside the fuel gage, which continued in cars with a tachometer (Rally dask, all Barracudas?) until ~1973. Yours should be the same as in my 1964 Valiant (photo) and 1965 Dart. I bought an adjustable limiter on ebay ~$30 years ago. Last pass, on my 1965 Newport, I got a generic 5 V regulator off Amazon which looked almost identical for $6. I should have paid $10 for an adjustable one. The voltage adjustment gives you one "knob" to tweak your temp and fuel level readings, but you need 3 more adjustments to get both correct at zero and full-scale. I've posted what I did (search).
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