Back left running light

We are assuming that you have checked the fuse ... right?

Normally not the fuse, but a tail light bulb may be burnt out. Replace the tail light bulbs, both sides.

Also it could be just a bad connection, you would have to trace back to the plugins to take them apart and clean. Try moving the bulbs around in the bulb sockets to try and make contact.

I all ready did all that and nothing still.

It is handy to have a test light for tracing the power, to see where it ends.

I have the same issue with my 2012 ram 1500. Left rear running light is out. Licence plate lights too. Checked every fuse, new socket and changed all the lights. Been pulled over 4 times with a verbal fix it.. any suggestions on what it is let me know.!!