It's black, about the diameter of a pencil. Attached on one end to the ground lug under steering column. It's about 2 1/2 feet long. The unattached end had a female spade connector. Looks like it goes somewhere in the center console. Any ideas????

 

Probably for a former stereo install, AFAIK all (factory) grounds in the 928 are brown.

 

You are probably right. I found it when I removed the old Alpine stereo to put in the Nak.