What if you increased the Tesla's albedo to the maximum level, or covered it in iridium panels? You could probably see it as a point source when the angle of the sun was right, pretty far out there in its orbit?

So let's assume the Tesla is half the distance to the moon and roughly the same albedo, and since the differences in distance to the Sun are negligible, both objects have the same surface brightness.

The moon has a diameter of about 3.5 million meters.

The Tesla is 4m long in its longest dimension. To make the math simple, let's say it can be modeled with a 3.5-meter sphere.

That means the moon is 1,000,000 times wider and has 1,000,000,000,000 the radiating area if we approximate it with a circular disk. The Tesla is half the distance, though, so we can divide that advantage by four, leaving us with 250,000,000,000, or 2.5x10^11. That's about 28 magnitudes difference in brightness (1 magnitude is about 2.5X increase in brightness). If the moon is -12.7, that still leaves us at magnitude 15 or so, which ought to be about at the grasp of a 14" telescope. Changing the albedo isn't going to change the brightness more than a couple of magnitudes, I would think.

So at present, it seems to me that it should still be bright enough to be seen.

However, it's going to get much, much farther away. The moon is less than 1% the earth-sun distance (1AU), and the Tesla's elliptical orbit will take it as far as almost 3AU from the sun (or almost 4AU from Earth at the farthest). A 2AU, the Tesla would be 775 times the distance used above, making it roughly 600,000 times or about 14 magnitudes dimmer.

At least that's the back-of-napkin estimates I get with my (currently) flu-addled brain.