Jumping tach, G light flashing and smoke through the defrost...

[Coach House 911]

After a summer of driving my '79 SC with no issues, all the while having the G- dash light flutering bright to dull on and the tach jumping eratically, last week small puffs of smoke rose from the left defrost. It was hardly noticable however soon after driving the smell of burning rubber became obvious.
I then drove home and garaged it and have not started it since.

Does anyone know if it is the alternator or possibly the regulator and a way to determine which?

Thanks,
Mike

[Coach House 911]

Will do immediately.

Thanks Grady