i have an installment sale for a business (i.e. equipment and Goodwill). after 1 1/2 years the buyer defaulted on the sale. I have nothing to repossess, because the buyer sold or disposed of the equipment as well. So now i have a loss that i am not sure where to report it. i have another business but it doesn't belong on that unrelated schedule C as a bad debt. I can make this the final year of installment sale with no income, but it doesn't take care of my loss

the loss needs to be reported on Sch D of 1040. Since you were not in the business of lending money. The loss is not a loss on an installment sale, but rather a worthless note