Maybe a little late - but for those that are thinking about trailer hitches - most software at dealerships on TALON report directly to HD. Once your newly warrantied bike is recorded with a trailer hitch your warranty is null and void on mostly all driveline components and wiring.
This also relates to HP items added to your bike. Dealerships vary with how they handle this internally so this may vary to who you do business with.
Dealerships do not determine warranty - HD does - Your local dealership may have coop $'s for those valued customers they wish to help @meaning those that continually do business with them.
MOOT POINT!!!
With all the aftermarket engine stuff and and general monkey around an owner does with his HD - it's no wonder the moco disallows a lot of general warranty work

I've had a tralier hitch on all my bikes for over 10 years and have never had any problem with getting any thing covered under warranty That includes 2 HD's
If it was the case All auto dealers would void any car or trunk with a hitch that was not Factory installed with a towwing package - So I call Bull $hit on that - Put your hitch on you've already ripped off the stock pipes and removed the O2 Senors (example) and god know what else.