Is the mobility scooter lift for a vehicle deductible

[Phillip1]

Yes. This is a deductible medical expense. See the following from IRS Publication 502:

Car

You can include in medical expenses the cost of special hand controls and other special equipment installed in a car for the use of a person with a disability.

Special design. 

You can include in medical expenses the difference between the cost of a regular car and a car specially designed to hold a wheelchair.

Cost of operation. 

The includible costs of using a car for medical reasons are explained under Transportation , later.