Fixed my lack of main indicator by installing an axillary automotive relay at the fuse block location.

The aux relay connections are pins 85 and 86 for the coil power.
Pins 30 and 87 are the circuit contacts.

Powered the aux relay from the LH main beam circuit at C0586-14 on the back of the fuse block. This circuit is fed from fuse F3 for + Vdc. The relay coil circuit ground (-) is attached to the fuse block mounting bolt post.

The + Vdc relay coil connection is jumped to pin 87 on the relay to provide power to the indicator lamp when the relay changes state.
Relay pin 30 is now connected to the intercepted Blue/gray wire from C0590-5 using an in-line fuse assembly. This wire remains connected to C0230-3 at the instrument cluster.

The in-line fuse should be rated at 0.2A - the indicator bulb is rated at 2W.

Mounted the relay to the fuse block mounting post and secured everything with mounting bolt.

Result!