The cost for the Section 179 deduction is 48,000. Interest on the loan is a business expense. How you record the trade in value as contributed capital to the business depends on the type of business it is.
There are limits on the Section 179 Deduction for vehicles.
The chart below from
https://www.irs.gov/publications/p946#en_US_2017_publink1000107705
shows that the maximum is 11,160. Since you reported that it
is 80% business use, the Section 179 deduction is reduced to 8,928.
In addition to the Section 179 deduction, you might be eligible
for "Bonus Depreciation", which is up to 50% of the asset cost. Bonus
Depreciation is taken after the section 179 Deduction and before the yearly
amount.
https://www.irs.gov/forms-pubs/about-publication-946
One does not cancel the other out.
