i have hooked two different trailers up to my truck. all the lights on my truck work as well as all the lights on the trailers except for running lights. i have marker lights,blinkers,turn signals,and brake lights on the trailers but no running lights. checked all the fuses and they are fine. i was wondering if anybody had this problem their self,etc and could point me in the right direction before i get started on this project. thanks

 

try a 12 volt tester at the plug then go from there