On Thu, 15 Jan 2004 16:44:35 -0600, "Steve Nosko"
wrote:

Seems to me there's a way to use a moderate current and sense the
_magnetic_ field. Follow the field around the board along the runners.
However, I don't remember what was used to sense the field.

HP used to make a hall effect (IIRC) probe for current tracing. One of their
Bench Briefs technotes described the probe and the process.