'67 Dart - No stop lights, turn signals on but don't flash

Hi,
I'm not good on electrical fault finding, can you lend me some help please?
My turn signals stopped flashing, left and right lamps come on when selected but are on solid. I noticed on the dash D-C ammeter that the needle dips slightly for the turn signal current, left or right, but not when the brake pedal pressed; checked and no stop lights.
The bulbs are all incandescent and I have tried a spare flasher unit, no change.
I have added ground wires to each rear bulb socket, as read here that ground may be cause of non-flashing but no change.
Since I've had the Dart, the ammeter has always showed a high charge level, not pegged but closer to the RH side than to the centre; not sure if that could be a contributor.

I'm not clear on how the turn/stop circuit works, it's a mystery to me.

Is there a simplified turn/stop circuit diagram or explanation available on FABO?

Does this 'no stop, non-flashing turn signal' point towards a particular kind of fault?