Michigan didn't get heavy industry because of cars. It got cars because heavy industry was already entrenched.
Cars didn't start in Detroit, cars were made everywhere. Every major city has at least one automobile factory still standing. Detroit won because of its underlying industrial prowess, and its access (via lakes) to natural resources in the Upper Peninsula and Ohio.
Heavy industry got entrenched because Michigan has really superb run-of-river hydro just all over the place. Seems like every town more than 150 years old has a dam or former dam, and factories along those dams. Not just grist mills either - factories were built downstream of the dams, and the waterwheels ran the mainshaft - from which lathes, mills, drills, cutters and other machines took their belt drive power. Only when factory expansion exceeded river capacity (as in, say, Ypsilanti) did they move to steam power.
It also had first rate transportation not only because of not only lake and river access (not so much on canals), but very early development of rail in the territory. Only six years after the first train moved in Baltimore, one moved in Michigan. Its rail system was isolated, like Alaska's, for 25 years until eastern railheads finally conquered the Alleghany mountains and plugged in. Michigan's lines were built standard gauge. Meanwhile it was breakbulk loading onto ships to cross Lake Erie, barges to sail the Erie Canal, etc. And that kind of work makes more sense with high value merchandise.
Today, it's the same. The mind blows at just how much stuff you can get made in Michigan. There is manufacturing capability like nowhere else in the world. Stuff you can't get done in California, five companies can do it in Michigan or northeast Ohio. Yes, the gloom-and-doom is true, industry has been decimated in the state several times over. But there was so very much in the first place that what remains is still the envy of the world. Almost every world automotive company has its design bureaus in metro Detroit, notably including companies that do not sell cars in first world nations. That's because of the ease of prototyping almost anything.
So if not cars, it would have been something else manufacturing-heavy.
Here's the bottom line. If your alien spaceship is sputtering and you need to land to make repairs, set down in Warren, Michigan, just north of the D. Everything you need to fix the ship can be fabbed within a 30 mile radius.