Very smart! Correct, you want to report the actual sale on one of the businesses. On the other business, you can mark that you converted it to personal use. There is no sale involved and the car is properly marked as being disposed.
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Technically, you'd show the vehicle removed from each business for personal use. Then report the sale of that vehicle in the investment's section so you can account for the depreciation.
But I can tell you right now that it's not worth it. Just remove the vehicle from both businesses for personal use and leave it at that.
Reporting the sale only allows you to deduct the "business use" losses from the business income, and those losses are generally to little to be worthwhile. (assuming less than 100% business use of the vehicle) Additionally, when you sell a used vehicle, even taking into account the depreciation taken on that vehicle, you're still gonna sell it at a loss. Losses on the "personal use" side are just flat out not deductible at all.