Were is the rpo relay located . my regular brake light don't turn on. i check light bulb r ok. there is no power to going to the back lights

There are 2 fuses for parking lights left and right side. so it can be 2 relays. located in the box in the front.

check relay in fuse block under hood

I assume the fuse has power if the hazards work.
The third brake light skips the turn signal switch, the regular brake light circuit goes thru the turn signal switch.
Do you have power going into the turn signal switch on the red lite green wire from the brake switch ?

The circuit goes from the brake light switch thru the turn signal switch and uses the same bulbs as the rear turn signals. I would check for power in and out of that switch next.

try cheaking the light switch its self may be faulty not normally a relay for but it shold tell you on fuse box which relay runs light ign ect

Have yoiu changed/checled the lightbulbs? (In other words,do your turn signal lights work? If the front turn signal lights work, but the rear don't, then turn on your four (4) way flashers. If the rear lights still don't work, then all the bulbs are bad. It is rare for all the bulbs to be burnt out at the same time, but it does happen.

If the turn signal/four way flasher lights work, then you probably have a bad brake light switch. However, first check your owner's manual to make certain there is not a separate fuse for these lights. If there is, then swap the fuse for the brake lights for another fuse (or relay) of the same size/amperage. (Facing the hood, the power relay box is located on the right side (usually) under the hood.)

The fuse box is located under the dash, on the driver's side of the car. Usually there is a plastic cover that has to be removed to access the underside of the dash, and then there is a plastic cover that has to be removed to access the fuse box. If you don't have an owner's manual, nprmally the fuses and power relays are normally marked on the plastic covers your remove ot access the fuses and power relays.

If the fuses/relays are good, then you have a bad brake light switch. This is located on a bracket just above the brake pedal. When you push the pedal down, the switch makes contact. Disconnect the plug to the switch, and jump across the plug contacts (not the switch) with a small piece of wire, or if a piece of insulated wire is unavailable, you can use a paperclip, you won't get schocked, just make certain that the paperclip does not come in contact with a ground while you have it plugged in to the plug for the brake light switch.

If the lights stil dont work, check for power to the plug for the brake light switch. If you have power to the plug, the turn signals and four-way flashers work, then my guess would be that you have a broken power wire (probably iside the steering column, or a bad turn signal switch. If the brake lights work whe nyou jump out the brake light switch, then the brake light switch is defective.

How they work can be totally different depending on the Year, Make, Model, Engin Size, and Transmission Type of your vehicle. Some vehicles have relays to control brake lights, some don't. Some brake light circuits go through the turn signal switch and some don't. Some are computer controlled and some are not. Since this information is missing from your question, nobody can say for sure.

OK try this, push and hold brake then push on the hazard switch if brake lights come on then replace the turn signal switch.

Troubleshooting Procedures - Read Completely Before Beginning
(American Car) All Brake Lights Not Working

• Check System Fuse: A fuse is used to protect the brake light circuit from amperage overload. If the fuse has failed it will not allow the electrical current to continue to the brake lights. To check the fuse, first locate the brake light system fuse in the fuse panel which is either under the dash or under the hood in the power distribution center. Connect the test light to a ground like an engine or dash bracket and turn the ignition key to the "on" position. Using the test light probe both sides of the fuse. If the test light illuminates on both sides the fuse is ok continue onto the next step. If one side of the fuse illuminates the fuse has failed and needs to be replaced. If the fuse fails as soon as it is replaced or when you apply the brake pedal the brake light electrical circuit is shorted to ground. Rarely a system short can occur, a car repair manual is needed to find the wiring schematic for the brake light circuit. Once the brake light wiring has been located inspect and repair as needed.
  
• Check Brake Light Bulbs: All cars have three brake light bulbs that create the brake light illumination affect. If all of these brake light bulbs fail no brake light operation will occur. I know what you're thinking, you might say all three brake lights at once? But in reality one brake light went out at a time and you did not notice. People only tend to notice something when they almost run into the back of your car to help persuade them to inform you the brake lights aren't working. Remove any of the brake light bulbs to confirm the bulb is ok or burned. After the bulb has been removed inspect the filament and replace if failed. If the brake light bulbs are ok continue to the next step.
  
• Checking the Brake Light Switch: A control switch is used to connect the brake light electrical circuit. This switch is located near the brake pedal lever. Basic switches have just two wires, power in and power out to the turn signal switch. Use a test light that is grounded and with the key in the "on" position test for power at one side (wire) of the switch, then press the brake pedal while testing the opposite side (wire). It should illuminate the test light, if electrical power is connected through the switch go to the next step. If no power is detected through the switch the brake light switch has failed and replacement is required. If your car is equipped with more than two wires integrated into the brake light switch a car repair manual is needed to locate the proper brake light circuit wiring.

It could be the brake light switch that is bad. that is located under the dash behind the pedal, the pedal presses the switch and turns the brake lights on.