1970 Rallye Dash Temp Gauge

All the gauges in 70 Dart 340 were working properly last year. The car sat for several months and now only the temperature gauge doesn't work. I grounded the sending unit plug using a test light and it flashed dimly about once every second. When I directly grounded the plug the temperature gauge needle moved less than a 1/16 of an inch. I tried this several times but the needle moved about the same distance each time. Is there anything I can try to get the gauge working short of taking the dash apart?