I traded in my car 2018 and bought a new one. I use the car for 80% business. I received 7k for the car and that went to the new one. How do I enter the sales price.

enter the full sales price  and then check the gain

say original cost $25,000 business depreciation was $13000.

your business basis is $25,000* 80% = or $20,000 less business depreciation of $13,000   net business basis $7,000

80% of $7,000 sales price $5,600 allocated to business so   loss of $1,400 

20%  personal = $1400

personal portion $5,000 less depreciation computed based on IRS tables for persona mileage gives you net value personal portion  if net value greater than $1400 the loss is not deductible 

what's bass is that TT probably can't handle this 

purchase price was 23,755, I received 7k and used 80% for business. so my sales price was 5600
I didn't take any depreciation

what is my
Basis for gain/loss
Basis for ATM

I follow the business portion of this answer, but not the personal portion.  My understanding is that the gain or loss on the business portion is reportable, but only a gain on the personal portion w/be reportable (i.e. cannot claim a loss on the personal portion).  The Recommended Answer seems to imply that if the "net value personal portion" is less than $1,400 then the loss is deductible.  I'm also not sure what the "net value personal portion" based on the IRS tables for personal mileage is supposed to represent?  I thought the personal portion would simply be 20% of the sales price = $1,400 - 20% of the original cost = $5,000, so net loss of $3.6k which would not be deductible.  Can you clarify?

You can no longer roll a traded in car into the new car basis ... it is a straight sale of the old and purchase of the new asset.