On what form of the 1040 do report rental income received for heavy equipment I rent to my S-Corp?

Rental income is reported on Schedule E.
Since it's not an arm's length relationship (you are a related party to your S-corp), you should see a tax professional to make sure you are claiming fair rental value and not giving the S-corp a discount on rent.
You also should see a tax professional because you need to properly depreciate the asset. Otherwise you'll have serious consequences in a later tax year and it'll be too late to get a refund.