Hi and welcome to the club. How do you like the A14 engine?

The later 620 alternator is a direct swap for a 1200 (A12 engine). The A14 uses a larger alternator than the 1200/620.

All FN alternators are, by definition, for use with external regulator. But there is a an internally-regulated A14 alternator with LS wiring. It uses the same T-connector: 1978-1982 internally regulated A14 alternator

But you have it wired incorrectly. FN type should be: F goes to a voltage regulator, not directly to the warning lamp. LS type can be connected directly to the warning lamp, but it is the L terminal. So you'll have to re-do the wiring (all two wires).