Typically, there is a wiring kit that compensates for an amber turn, red brake and running lights. Once wired in, the control box does the math and makes everything work. I'm guessing it may not have been available for the Fiat, or you've used the wrong the kit. Etrailer is great, give them a call and tell them that you have separate brake and turn signal lights. They should be able to fix you up.
Don & Mary
2019 Newmar Dutch Star 4018 (Freightliner)
2019 Ford Raptor