1970 Volkswagen Beetle Fuel Gauge works sporadically

Electrical problem
1970 Volkswagen Beetle 4 cyl Two Wheel Drive Manual 99999+ miles

I have owned this bug for 4 years, and the fuel gauge has worked for only a very short period of time when I first had it. I recently replaced the Speedo/Odometer assembly (with a used part) and the fuel gauge worked again for a short period of time. I replaced the wire from the fuel tank to the gauge, as well as the vibrator (new part), and it now works on and off; usually when in warm weather - in the morning, no gauge, but in the afternoon, it works sometimes.
I assume that it is the fuel sender at this point, but was wondering if the issue of warm/cold behavior indicated anything else - the temperature refers to environment temperature, not necessarily whether the engine is warmed up or not.