(ET) Model number suffixes

[Geoff Rich <grich firstsolar com>]

Hello all,

I recently got a copy of the Homeowner's Service Manual from Bill.  I'm 
curious about all the two-letter suffixes in the model numbers, which seem 
to identify significant changes in the tractors' designs.  For instance, I 
have an E16AA, and was recently talking to a friend with an E15 who wanted 
to sell the machine to me for parts.  From a quick glance through the 
manual, it's clear that these machines have several major differences in 
the control circuitry.  Thus the E15 would be pretty good for mechanical 
parts, but lacking in some electrical control parts.  Previously, I had 
thought that they were pretty much the same.

Circuit boards appear, change, and then disappear in some machines like 
the 
E20.  Has anyone every tried to list the changes?  I'm sure Bill has this 
all in his head, but it would be nice to to have an annotated list of the 
machines and all their various versions.  I may be able to do this if 
there 
is sufficient interest, but it seems likely that someone has already done 
it.  It appears that all of the answers should be in the manual, but need 
to be sorted out.

Thanks for any help the list can provide.

Geoffrey Rich