Been having some electrical issues with my 79 b310/210. The alternator light stays on almost all the time. I checked them with a voltmeter and reads between 12.3 and 12.6 volts whether its running or not. Park lights only turn on when the car is running. Both the alternator(replaced today) and battery are new. What do I check next?

regulator,
wiring...

1979 B310 USA (Datsun 210) is supposed to have an alternator with built-in regulator. If intstead you were sold a B210 alternator in it won't charge correctly

Examine the alternator, the back should have 'S' and 'L' terminals


If the T-connector is marked 'F' and 'N' that's the wrong type




Also the METER Fuse in the Fuse Box must be good, and the CHG light in the dash must be working. If it is burnt out, the alternator won't charge

Finally the Fusible Link is how power gets from the alternator to the battery. With the engine running, if you get 14 volts at the back of the alternator (big A/BAT terminal with large white wire) but only 12 volts at the battery, that's the problem. Check the small white wire -- if it is zero volts it means it's not getting 12V from the other Fusible Link wire