there may be a short
get longer wires
You have a poor or no ground between the vehicle and trailer.
Tail lights and brake lights fuse.
On a toyota tacoma 2003 SR5 when the tail lights are turned on the brake lights come on and when the tail lights are of the brake lights work just fine what could be the problem. If the truck has a trailer plug, inspect the plug and plug wiring for damage and corrosion.
short circuit on trailer light wiring
There are no extra fuses for your trailer lights. If you have the towing package (and you do) the trailer lights run through your regular fuses (tail, brake, turn).
i got a 2006toyota highlander my tail lights dont work but,every other light works please help me
Brake lights and turn signals are on a separate circuit from the tail lights. Tail lights are on the same circuit with the dashboard lights. If the dashboard lights aren't working either, check the fuse. If they ARE working, check the headlight switch.
If the headlights are on and brake lights work but not the tail lights, it is possible there is a short in the electrical wires. Another cause for this could be that the tail light bulbs are burned out. Most vehicles have more than one bulb inside the tail lights to control different lights at the same time.
Try the tractor with a different trailer, the pig tail is most likely not connecting properly.
I would first check the grounding between the truck and the trailer. If the ground is good then bulbs would be the next thing to check.
changed brake light switch at pedal and still no brake lights
You do not have the trailer lights connected properly.