LED discussion is a bit off-topic but I can tell you this for certain with my 2002 Focus:
Installed LED replacements for the 194 bulbs in the HMSL and for the license plate light bulbs. Worked fine, no issues.
Bought some LED replacement bulbs for the taillights after the housing overheated and the incandescents were burning out every few months. Replaced taillight socket at same time.
Cruise control quit working - no indication why - just nothing happened when you pressed the button. Suspected the brake light switch and ended up destroying it, but was able to rebuild it. Swapped tail-light and turn signal bulbs. Cruise control worked fine again, but turn signals hyperflashed.
Load Resistors would have taken care of both problems, but need to be mounted to metal and away from plastic and not much of that near the tail-lights and more effort than I wanted to get into, so ended up going back to standard bulbs.