How i can fix stop lamp??

Do you know anything about automotive electronic's ? The brake pedal position sensor is a input to the BCM - body control module ,the BCM turns on the stop lamps . Possible short in the (CHMSL ) - center high mount stop lamps , wiring etc.... Causing problem inside the BCM . Do you know what wiring diagrams are ? Free one's here http://www.bbbind.com/free-tsb Enter vehicle info. year , make , model an engine size . Under system click on lighting , then under subsystem click on exterior lighting . Click the search button then the blue link's . First diagram show's the brake pedal position sensor input to the BCM ,lower right . Second diagram show's BCM power supply to the third brake light (CHMSL) . Having a qualified repair shop with a professional scan tool to check for DTC'S - diagnostic trouble code's could save a bunch of time in diagnosing the problem .
DTC B3903
The body control module (BCM) supplies voltage to the center high mount stop lamp (CHMSL) and the powertrain control module (PCM) when the stop lamps are active.
DTC B3903 Stop Lamp Relay Circuit

Stop Lamps
The body control module (BCM) is responsible for controlling the stop lamps. When the driver presses the brake pedal, the BCM will receive a signal from the brake pedal position sensor. The BCM then supplies battery positive voltage to both left and right stop lamp assemblies and to the center high mounted stop lamp (CHMSL). The stop lamps are grounded at G401 and G403. The CHMSL is grounded at G302.

The brake light switch is an input to the BCM - body control module , do you know about BCM'S - electronic module ?
Stop Lamps
When the driver presses the brake pedal, the switch contacts open and battery positive voltage is interrupted to the BCM. The BCM then supplies voltage to both the turn/stop lamp supply voltage circuit and trailer rear turn/stop lamp supply voltage circuits. The BCM also supplies voltage to the CHMSL though a dedicated circuit.

could have DTC'S stored in the BCM
DTC B3445 00: Stop Lamp Circuit
Circuit/System Description
The stop lamp switch is used to sense the action of the driver application of the brake pedal. The body control module (BCM) provides a low reference signal and a B+ reference voltage to the stop lamp switch. When the stop lamp switch contacts close indicating the brakes have been applied, the BCM will apply battery voltage to stop lamp relay control circuit and the center high mounted stop lamp (CHMSL). When the stop lamp relay receives battery voltage from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage to the STOP LAMPS fuse to illuminate the left and right stop lamps.

DTC C0277 00: Brake Pedal Position Sensor Calibration Not Learned
DTC C0297 00: Brake Applied Output Circuit
DTC C0890 00: Device Voltage Reference Output 3 Circuit Voltage Out of Range

In the event that DTC C0277, C0297, or C0890 sets as current in the body control module (BCM) is an indication of a possible internal BCM malfunction or programming error. There are no external circuits available to diagnose on this vehicle with respect to these DTCs.
Your best bet would be to take your vehicle to a qualified repair shop or the Cadillac dealer.

Stop lamp switch may be sticking or broken Follow the brake pedal to where it makes contact with the switch plunger...its probably stuck in the "brakes applied" position causing brakes lights to stay on If not that, then it may be a bad ground issue at the light bulbs themselves

{: ) Did somebody worked on the BCM or your brake pedal? The wirings and connectors could have been knocked off. For the moment. let's just rule out the wiring issue first.
Under normal operations, the stop lamps get its power from the BCM (body control module). The BCM monitors the signals coming from the brake pedal sensor whenever you step on the brakes or not.
The component fix is to replace the brake pedal position sensor. I just hope your problem doesn't come to the point of replacing the BCM too (rarely happens).
But before proceeding with the replacement options, try to bring it to a shop with a GM scan tool and ask them to perform the brake pedal position sensor calibration. This is the quick fix without replacing any component. I hope you get lucky.

You may have another Alternator issue so get the charge rate checked. Then, look for a leakage issue like the glove box lamp staying on, or the lamp in the trunk or boot staying on. I have even seen the lamps in the footwells stay on and drain a battery overnight.
An easy test is to use a test lamp. Make sure all the doors are closed and everything is turned off (tail lamps etc). Disconnect the battery negative and connect the test lamp between the battery post and the cable clamp. If the lamp lights and stays lit, you have a leakage. Begin by disconnecting the courtesy lamps or removing the bulbs. When the test lamp goes out, theres ya leakage. If you have a charging system connected to the vehicle which charges a second battery, like one in a caravan, check those circuits too.. And even though the Alternator is new, it may still be the cause of the problem.. So check it out as well..

Try adjusting your brake light stop switch..it is located on the upper side of the break pedal...Now you also may just need to replace it, if adjusting it dint work...All you have to do is untighten the screw, and unplug it, and mve it backwards or forward a little...make sure you plug it back up, to test if it is working correctly, and then once you get it working correctly, go ahead an tighten back down the screw...Goodluck...

Brake switch (stop light switch). need to be replace
you can find it on the brake pedal.

let me know

Check the lamps first to see if both are good, do a wiggle test to see if the lamp's socket is good(sometimes they get too hot and the contacts spread open). Next check fuses for the running lights and break lights. If the running lights work on the front but not on the back then its not a fuse its a ground issue. Use a stick or another person to depress the break pedal to check for power at the plug that goes to the stop/running light lamp.

Sounds like that the brake sender diode/relayis faulty, these are under the brake pedal in the front of the car, usually and easy fix

It sounds like the catalytic converter is plugged