Wiring diagram for 2000 chevy silverado 2500 tail lights

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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?

disconect the reverse light switch wires from the gearbox & bridge. If the lights come on it is a faulty switch.

Yes I would look for a ground circuit problem. I would look at the ground wires for the headlights first. Even run a new ground wire for the tail lights to see if it helps.
Could be a ground connection for the body to frame or body to battery.

I HAVE 2000 BLAZER and the 3rd brake light works but the ones in the tail light do not work have turn signals and new bulbs but no brake light

check for power at the wires going intop the tail lights, real common that the circuit board is bad, but unlikely both at the same time. The tag, tail lights and brakes are 2 different systems. Do the turn signals work normally? if so the wiring from the turn signal switch to the brake lights is GOOD. the stop light switch had\s a ORANGE wire that should have 12V if not ck STOP LPS fuse, when brake pedal is depressed, the WHITE wire is 12V (at the stop light switch) if that is OK, the turn signal switch COULD be bad. The wiring harness plug is near the back left under the tailgate, see if that is disconnected?

Standard wiring colors are as follows:

4-Way

5-Way

6-Way

7-Way

Green

Yellow

Brown

White

Red

Blue

Purple

Right Turn & Brake

Left Turn & Brake

Tail Lights

Ground

Backup Lights

Electric Brakes

Auxiliary Power
Green- Right Turn and Brake
Yellow- Left Turn and Brake
Brown- Tail Lights
White- Ground
Red- Reverse (Back Up) Lights
Blue- Electric Brakes
Purple- Auxiliary Power

It sounds like your green and yello wires are shorted together somewhere along the length of the harness. I would check the wires on the trailer first. Easier yet, if you have another trailer to connec or access to another to use for testing, connect to it and see if the problem repeats; if it does the trouble is in the vehicle's wiring.

you have a bad ground to the taillights , the signal is looping back to the front light grounds

same bulb but 2 seperate elements. wiring diagram u should be able to obtain from your local auto parts store like autozone(preferred)

check fuse.if good you got grounding problems or faulty turn signal switch.

check grounds on rear light assy's