Good question! I do not plan to add the front ID lamps but did look up the Federal requirement. The short answer is the front and rear center ID lamps (amber, red)
are required on 80" wide trucks, etc., but on trailers only the rear ones are required. Turn signals are the same, on trailers only the rear ones required. Other lamps
not required on a trailer are backup lamp and of course headlamps.
The front and rear clearance lamps (amber, red) on 80" vehicles are required on trailers as well as trucks, etc. I believe having both the front and rear ones on the
fenders, facing forward and rearward, is good for a trailer if that is the widest point.
If anyone wants the long answer

this is a link to the Federal regulation about vehicle lamps and reflective devices. Two tables pertaining to 80" wide vehicles
near the end are relatively easy to read. Tables I and II begin on Page 310 of the regulation or in this PDF version on page 72 of 75. Other tables pertain to more narrow
vehicles or motorcycles.
http://www.unece.org/trans/doc/wp29compendium/5-1.pdf
Sorry about this rather cumbersome link. It is included just in case someone wants to see the actual Federal regulation.
Bill