Tail light's will not work

Try replacing the turn signal flasher. Make sure to use a Heavy-duty flasher. Hope this helped.

Check for that fuse in a fuse panel under the dash.
That second wire from the old light is a ground wire, whereas the new light's socket is case grounded if there is no ground wire for the light. If the fuse for the tail lights is good, check if the tail lights lost a ground .

Do you doing this right.Turn on[no start].Wait for signal.

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Did you check the park fuses, note the diagram, rr and lr. Use a test light to check voltage at fuse circuit, headlamp switch on. That should tell us if problem is before the fuse or after.
You always want to check voltage and ground circuits, for lamps. Do the front park lamps work?

I've worked on these the first drove me crazy. its the turn signal switch every thing runs thru these. head lights, turn signal, brakes. except the third brake light. it runs directly from the brake switch. go figuare

The best thing to do is check with a test light on the outlet of your pickup where you connect your lights and turn you key on without starting it and turn your turn signal on right or left and probe the prongs and see if there is one flashing. Do the same with the other flasher and make sure at least that is working. If not let me know back.

check fuse's, if that doesn't work check bulbs

you prob got a trailer plug prob bad wires if not tail lights run through turn signal switch tell fix ya bout me ok

just takes a tester and some time

I am having the same problem on an 04 2500hd there isa 15 amp stop light fuse inside the cab on the side of the instrument panel and a 25 amp stop light fuse under hood. you could also have a break switch issue the switch is located up on the break pedal linkage you should have power on the white wire when you push the pedal in (check with a test light) in my case I have a broken wire along the frame rail in the harness it is a light blue wire,