Hyper flash - but only one?

One for the brain-trust.

I was putting LED bulbs in my turn signals (Alla Lighting brand) and discovered my right taillight assembly is practically brand new. Left one, obviously not.

I installed the bulbs and left one works fine, right (new) one hyper flashes. I know I'll need a resistor but why would the new one need it and not the original?

 

Is the rear taillight assembly you replaced from a truck with LEDs? They came in I believe 2009+ vehicles.

 

I got the truck used and the assembly was replaced before I purchased it. I think both of them have LED brake lights/taillights but the turn signals and reverse bulbs are incandescent. Whatever the combination, they're the 2014 taillight assemblies.