I purchased a conversion vehicle for my wife in December, my wife is wheelchair bound and cannot drive a normal vehicle. The conversion cost about 40k. Can I write it off

Certainly! If you’ve purchased a conversion van due to your disability, there are tax deductions you may be eligible for. Let’s break it down:

Wheelchair Van Conversion: While the van itself is not tax deductible, the conversion features are. This includes the cost of:

Wheelchair lift
Hand controls
Securement devices
Trackless transfer seat 12.
What Is Considered Tax Deductible? You can include in your “medical expenses” the difference between the cost of a regular car and a car specially designed to hold a wheelchair. Most of your deduction opportunities will fall under this category of medical expenses. However, you cannot include depreciation, insurance, general repair, or maintenance expenses. Additionally, travel to and from work is not deductible, even if your condition requires non-typical transportation.

Example Calculation:

Suppose you drove 1200 miles for medical reasons in 2019 and spent $300 on gas, $10 for oil, and $200 for tolls and parking.
Actual expenses (gas, oil, tolls, parking) = $300 + $10 + $200 = $510.
Standard medical mileage rate = 18 cents per mile. Multiply 1200 miles by 18 cents = $216.
Add tolls and parking: $216 + $200 = $416.
Since $510 is more than $416, you would include $510 of car expenses with your other medical expenses for your 2019 return 1.
What Is NOT Tax Deductible? Expenses that do not qualify for deductions include:

Travel for purely personal reasons (e.g., vacationing while receiving medical care).
Travel for general health improvement.
Operating a specially equipped car for non-medical reasons.

source includes IRS PUB 502

The base price of the van is not an eligible medical expense, but the extra cost of converting it is an allowed expense.