Our tow vehicle needed a new battery this winter.
When DH replaced it the brake controller gave an error code which we knew was that a trailer was not attached. LOL! We knew that. It has been in storage since November.
Today our tow vehicle brake lights were flashing similar to hazardous lights. The brake controller was clicking.
We didn't want to run down a brand new battery so we disconnected.
If it’s a Ram, check the brake light switch. Common failure but easy to replace. Will flash CF on the factory brake control and give the trailer disconnected message. Cruise control will also not work. Sometimes you can pull the plunger on the switch out - it kind of ratchets and locks in a longer extended position. If that works, change the switch anyway as it will fail again.
It would help if you posted year, make and model of vehicle, since you didn't list it in your profile.
Dan-Retired California Firefighter/EMT
and Zoe the Wonder Dog(R.I.P.)
2016 PrimeTime TracerAIR 255, pushing a 2014 Ford F150 SCREW XTR 4x4 3.5 Ecoboost w/Max Tow Package