I did car wash installation and repair for a few years in San Antonio, Texas. I worked for the Dilling Harris Distributor there.in the 1990s, D/H was probably the best self-serve equipment manufacturer in the business. They partnered with a Michigan Company, GinSan Electronics. Unfortunately, they hired a shister as General Manager and he took the Legacy that Harry Dilling and Joe Harris started and ran it into the ground. The company finally closed and Joe Harris' son took it over, but I don't think he made a go of it either. It's a shame. I owned a 5 bay self serve in San Antonio for a few years. I maintained all the equipment myself and loved the business (or hobby, I should say....never made any money).
If you're thinking of buying a car wash, the key thing to remember is that if you keep things clean, give people a good service for the money you are charging them and keep everything WORKING, people won't get frustrated and tear your equipment up. It is not a hands off business. You have to be aware of how everything works in every bay and fix it before it breaks.
Having good chemicals is another key. The chemicals that D/H sold when they were in business were the best I ever used. PureGold was amazing and their wax was good as well. I am extremely nostalgic about D/H GinSan. I would work on one of their systems in a heartbeat. They are well-made, logical and simple. I don't imagine there are all that many left, but they were awesome back in the day.