You're right. OEM on FLSTC 99 signal cancel is as you say, speed and duration.
Does anyone know how to make the turn signals on my 99 FLSTC Heritage cancel they way they do on my 2005 Sportster XL883C, which is cancel after returning to vertical after leaning over in the turn.

Does anyone know how, or how to find out?


ps The following was posted on XLForum.net by IXL2Relax:
Starting in 2004, the Sportster Turn Signal Module TSM included
the Bank Angle Sensor BAS-
That is what allows the cancellation after a banking turn...
If you were to connect an external BAS to the Heritage,
you would need to find a way for the TSM on that bike
to respond to the external BAS signal...