1977 targa charging

[7783911]

I ve noticed that my targa doesnt start charging the battery until i exceed 2000 rpm

I thought i read somewhere this is normal?
If it is..why would that be the design?

If not..is the culprit the alt lamp in the gauge not being correct wattage?

Reason i tested my new voltmeter and it confirmed these numbers

Thanks

[7783911]

I checked the wiring and redid the alt warning lamp connections and found one unclean connection which i redid and voila..that completed the circuit and charging is now occurring even at idel