After the main rear connector, where the majority of the circuits get to the back ( this is a 2001 MY part number, but the same location ) along with where the trailer tow connector plugs in :
there is another connector C405 that the trucks circuits are at.
This connector the left is pin #4, Light Green w/ Orange stripe wire.
I would image that the wire is broken between C405 and the bulb connector ?
This is a SWAG, does the parking lamp work on the left side, or is that also out ? ( the thread only mentions the Stop / Turn circuit ).
C405 is a common connector that the stop / turn, park, reverse circuits all share, and is in the rear of the truck.
The Truck's stop / turn lamps are in the fuse slots for the trailer tow stop turn, on the supply side of the fuse. Same circuit from the MFS branches off prior to the trailer tow rear turn signal fuses. The left trailer tow fuse is F42, if you want to try a meter here. Next spot would be at C405 at the rear of the truck.