only Marker rear lights not working

I guess I should have a little more precise on what I meant by "socket on the truck". You'll probably need the 7 way harness for the truck, which basically is a 7 way socket with a pigtail that connects to the truck wiring through a connector.

 

Likely just the 7 way plug. Undo two bolts and unplug it from wire harness. Plug new one in and away you go. 10 min fix.

 

Have you thought about buying a 7 way tester to narrow down the issue?

https://www.amazon.com/IPA-Tools-78...+tester&qid=1591403726&sr=8-3#customerReviews

 

And that’s why I’m saying it’s likely the plug. Stop and think about it. Marker/tail light circuits have constant power all the time while lights are on. That draws salt in. Signals/brake light circuits never ever fail as often.