Right Side Rear LED Running Light - Dim on one Side

CST_B320

Hey all, need some electrical advice.  Have a 2019 T@B 320S Boondock.  Recently the right rear red LED running light on the side of my T@B has either had problems turning on or now has dimmed and is very weak.  When I attach the trailer to the truck and run the engine, the light gets a little brighter but not much.  All the other LED outside lights on my T@B are working just fine.  I'm guessing the LED in question is beginning to fail but don't want to just order a new one if this is not the problem.  Any thoughts?   Also if anyone knows the part number of this red rear LED running it will come in handy if I do need to replace it.   Thanks in advance for all the help you can offer.  

  
Right side running light Connected to Truck with Lights on and Ignition OFF

 
Right side running light Connected to Truck with Lights on and Ignition ON


Left side running light Connected to Truck with Lights On and Ignition ON or OFF 

Grumpy_G

I'd guess it's more of a voltage issue, high resistance equaling voltage drop in the 12V feed or more likely on the ground side. It could be a problem inside the light assembly as well. Take the light off and check if a test light connected to 12V is dim as well (=problem on the feed side) or if there is a voltage drop between the ground at the light and the trailer frame. 

CST_B320

Thanks so much for your thoughts. I removed the light and tested both wires with a 12V test light and it was as bright as when I touched it directly to my battery.  So no voltage drop.  The light itself was even weaker today than yesterday.  It's dying a slow death.  I was able to find the exact replacement light on e-trailer for $12.74. (Part # MCL17RB) if anyone else needs one.  It's on it's way.  Thanks again for your expertise.