Just bought this lamp a few weeks ago, know it is from a T but I cannot identify the year.
16 to 19 all car 20 to 27 on non starter cars
From your profile it looks like this is your first posting. Welcome to the forum! There is an on-line encyclopedia that provides some good information on a lot of different T parts. The top page is located at: http://www.mtfca.com/encyclo/index.htm and the one for your lamp is located at: http://www.mtfca.com/encyclo/sl11a.htm
If you are interested in obtaining a Model T or learning more about them, I would suggest checking out one of the local chapters near you. Please see: http://www.mtfca.com/clubpages/chapters.htm and http://www.modelt.org/index.php?option=com_content&view=article&id=5&Itemid=15 They can be a real source of encouragement and help you in learning more about the Ts.
For Bob -- while I was looking at the light on the on-line encyclopedia, I noticed it listed 1916-1926. It was only in the early 1926 model year that you could still order a USA produced open car without the starter & generator. Now ton trucks -- from memory I don't know how they were or were not used on them.
Hap l9l5 cut off