It’s not the assembly, getting power to plugin...if getting power then what’s the problem? Have tried 2 new assemblies?!!🥴

 

Double check polarity? LED's only light up if the polarity is right. Don't know how it could have gotten swapped, but I suppose anything is possible? Maybe the connector's been cut off and reattached in the past?

 

Not installing used junkyard light, checked fuses and bypassing any other switch options. Direct connecting to regular brake light and dealing with dash oriented problems later. There has been some after market things done at dash point 🙈 one of which caused a complete mechanical failure and a wreck.😩