adrianv said:
Yes, I have power as far as the "LR PRK" 10 amp fuse under hood.
OK, so if there is power getting to that fuse, the fuse is good, and the bulbs are good, it has to be something in the wiring. My guess is a connector contact is loose or corroded. Your flickering symptom seems to also indicate that.
Attached is the wiring diagram for the tail lights. Click the blue paperclip link to see it full size. On another page, it shows the LR PRK fuse in the under hood fuse block, and it shows the circuit passing through a connector on the back of the fuse block. (Let's hope it's not there, for now.) From that connector, it shows the circuit going off page with the "M" label.
On this diagram, the circuit then comes in with the "M" label, passes through Pin G of connector C405, then through pin E of connector C402, then splice S417, and on to the lights. So, it looks like either a wire is broken, or there is a bad connection at C405, C402, or S417.
If the left license plate light works when the left tail light doesn't, then I would guess the problem is at or near C402. If the license plate also doesn't work, then the problem is probably at or near C405.
C405 is an inline connector near the left rear corner of the truck. It should be blue, and appears to be sealed. If you climb under the truck you should be able to see it near the frame rail. (At least that's what the book shows.) The brown wire (not the brown/white wire) is the parking lamps circuit. Disconnect this plug, check for clean contacts, and try measuring voltage there.
C402 is an inline connector near the left rear tail lamp. This is a grey connector, and I have seen it when I replaced my tail light assembly, so I know right where it is. If you remove the tail lamp (open tailgate and remove a couple screws) you will see a foot or so of wire attached to the tail light sockets, and then the C405 plug. The brown wire is the parking lamps circuit. Disconnect this plug, check for clean contacts, and try measuring voltage there.
If that does have voltage, then maybe splice S417 is open. This is a splice inline in the wires between the connector and the tail lamp sockets. If the break is there, it should be relatively easy for you to find and fix it.
If none of these have voltage, then it is either in the big red connector under the under hood fuse block, or there is a broken wire somewhere inside the harness under the truck. The left parking lights circuit leaves the fuse block in the red connector, on pin B1. This is a brown wire with no stripe, which is next to an orange wire. There is one other brown wire, but this is the trailer parking lights, and does not have an orange wire anywhere near it. There should only be one orange wire on the red connector, so that should make a good marker for the correct solid brown wire.
If you need any diagrams of the individual connectors, I can supply them, but it should be sufficient to just look for the brown wire.
Good luck!
-- SS