My advice is to look for a consultant.
The reason is the concept (add in-bay or offer hand wash or detail) would transform you from product to customer-oriented company.
Product-oriented (wand) tries to attract customers whose needs can be matched with “products” like soap, wax and water. Customer-oriented focuses on satisfying needs. The reason is satisfaction is prerequisite to customer retention which has positive impact on business results.
In short, wands are operated like
vending machines and in-bay, and more so, hand-wash and detail are contact sports.
A busy retail plaza may be a good site location for what you are proposing or not.
Have you prepared an estimate of market potential - what are total potential carwash and detail sales in the area?
This is where most folks begin solving location problems.