I was able to clear the clog with a garden hose. It was backing up when the automatic would run.
Google News: 1937-1961 car wash ads
Google scans random newspapers and make them searchable. I decided to look for some old carwash ads. You can search for your own at: http://news.google.com/archivesearch/advanced_search
The first ad was from The Evening Independent 11/23/1937. Captain Dunn’s Service Station, 9th St. and 7th Ave. No.
The second ad was from West Seattle Herald 6/30/1938. Al Roderick’s Texaco Service Station, Admiral Way at 42nd S.W.
The Third ad was from Pittsburgh Post-Gazette 3/17/1961. Natrona Hgts. Automatic Car Wash (Triple Check Car Wash) 2705 So. Park Rd. Bethel Park. Pa.