Aloha All,
Mine also is attached as Geo said, to the engine on the back side of the front plate to a through bolt for the timing chain cover. The frame attachment is on the rear side of the engine mount.
Here is what Triumph Register of America says in their judging standards, "Ground Strap. A round, woven steel, ground strap is attached to the timing chain cover and the front motor mount.
The purpose is to ground engine with body by spanning the insulating motor mount."