I got this idea from William’s comment last week in my easily confused words post. Lead and lead are spelled the same but pronounced differently depending on the context, as in “Lead on to the lead paint.” Or, phonetically, “Leed on to the led paint.” As you surely remember, I went over a similar situation with read and read. To sum up, read is pronounced two different ways because the word’s ancestor was, and the two pronunciations are used to distinguish two different tenses.
However, in this case not only are the tenses different, but we have a completely separate word involved. Lead the metal comes from the Old English lead and Western Germanicloudhom, which is thought to be from the Old Irish luaide(so from Ireland to Germany and back over to England!). The Irish word is thought to come from the Proto-Indo-European ploud, which means “to flow,” which only makes sense if they’re talking about molten lead, but who knows? It was kind of a long time ago (only about five to eight thousand years…).
The other lead (as in, in the lead) also comes from Old English, but a different word, laedan. This word can also be traced to Western Germanic, laidjan which means “to go”, and further back, the Proto-Indo-European leit, with the same meaning.
So as for the pronunciations and spellings, it’s all probably coincidence, just like in read and read. I blame the “ea” combination for having so many different ways of being said.