Believe (think the engineering drawings state it also) that the bronze was lead dipped. Over time the lead wears/is sometimes cleaned away leaving the base metal
That's an interesting concept, lead wearing. I would like to see a drawing or specification on the battery end connectors. I think that the copper ring lug end was dipped in lead and it was not an even coating. Lead is a fair conductor of electricity, not subject to rapid corrosion (lead does oxidize) and it is soft giving a flexibility when the connection is made to a lead battery post. In some feasability tests, I used a lead compound to attempt seal electronic component containers. Once the lead went on the container, it left a permanent residual layer that could only be removed by extreme heat, not an easy process.
That being said, I remember back in the 60's, changing battery cables because the battery terminal end connection corroded and often broke (read snapped) from being disconnected and reconnected. Those connections were "bronze" in color, and bronze, compared to lead, corrodes easier and is brittle. The steel bolts were another problem, all due to batteries leaking acid. I remember in the early 70's getting medical treatment from battery acid burns (read gangrene) just by rubbing my arm on the battery case.
If in fact the battery terminal end of battery cables are made from lead, someone better tell Kevin Marti and all the Mustang parts suppliers.
Jim