Get a ALLDATAdiy subscription for the Smart ED. The latest year that they have manuals for any Smart is 2014 which includes the ED. $29.95 for first vehicle/$19.95 for each additional vehicle per year.
i just checked my subscription and they do have chassis/drive train wiring schematics. They take a bit of work to decipher since they use those Mercedes Benz alphanumeric designations for every little electronic/electrical component rather than a description.
of course, schematics of the electronic modules themselves (like used to be attached to the back panel of home electronic appliances in the old days) are not provided - that's regarded as "proprietary information".