Yes, in your first business, EDIT your Vehicle Asset, and report that you 'converted it to Personal Use'.
Then enter your new vehicle as a Vehicle Asset for the first business.
For your second business, you can enter the truck as a Vehicle Asset. However, for your 'Cost' you will need to use the undepreciated amount, since you already claimed some depreciation on it for your first business.
If you claimed Standard Mileage for it, about .25/mile is depreciation. So if you claimed 10,000 Business Miles, for instance, you claimed $2,500 in Depreciation. Subtract $2,500 from the Cost you entered for the truck when you first started using it for business, and that is the Cost you will enter when you add the truck to the second business. There's a chart for each year on page 24, in IRS Pub. 463, if you want to be exact.
If you claimed Actual Expenses for the truck in your first business, you will see the Depreciation Deduction amount on your Form 4562 for each year. Subtract that amount from the original Cost Basis, and that's the Cost to enter for the truck in the second business.
Here's more info on Using a Vehicle for Business.
@jellsworth
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