76 TR6 Over Drive

[JDCampa <JDCampa@aol.com>]

My OD is no longer responding to the steering column switch and seems to
engage and disengage on its own volition.  If still on when I back up, it
makes terrible grinding noise.   A local mechanic says the problem not
electrical and I need to drop the tranny to get at the OD.
Any ideas?
Have I ruined the OD or tranny by backing up with OD engaged? 
If so, can I rebuild it?

Thanks