[tsubaki]

The problem that usually exists when hard wireing is the use of blinker and brake lights. NOTE that the trailer has a combo brake and blinker whereas most vehicles have a brake light and orange blinker, so a converter is needed. In some instances when the vehicle has a combo brake and blinker a converter is still needed because of the way the vehicle seeks power.
I have seen one instance where the owner did not want to purchase the T but did install the converter and still had problems, once he installed the T and harness all problems ceised.
And the possibility does exist that there may be a fuse just for trailer lights in the truck, under the dash or hood. A F150 we have has such a setup.