Follow up,
More research indicates that some later trucks (some Chev, GMC, Dodge and Mercedes) have something called a PWM (pulse width Modulator). If I understand correctly, it's job is to regulate voltage to LED lights and micro electronics, to make it more constant.
As a result, many Backup/rearview camera systems that wire into a clearance light do not/may not work without an adaptor.
Getting the impression that you can either spend $50 - $60 for an adaptor OR you can run a dedicated wire back to the camera.
Feel free to correct me if I am indeed, full of male bovine feces. :-D