Mike,

Here is a link to a scanned original 1955 Chevrolet Truck Engineering Features pamphlet that I came across.

After a thorough quick read of the document and the pics inside, I couldn't see anything indicating a "3rd" factory hole or a corresponding control/device in that spot.

Also could not find anything related in this '55.2 Truck Operators Manual

I don't have access to a '55.2 or later Accessories Installation Manual, but maybe someone else does and can search that to see if we are missing something here???

Sorry I couldn't be more help. frown

Dan

~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)