Does the brake light switch affect the transmission?

First you need to state the vehicle make, model and year. What was the original problem. A good mechanic will mark hoses before disconnecting them. The transmission speed sensor will affect cruise control, not the ABS function. The application of the brake pedal will drop the cruise control, Possible brake light switch problem. Perform an ODII scan for any stored speed sensor faults. Use the OBDII scan as your guide to any repairs, to avoid buying parts you don't need.

year/make/model?? The brake lights are controlled/activated by the brake switch attached to the brake pedal. This switch if defective will affect the operation of the brake lights. On some makes/models, the brake light circuit also runs through the signal light switch which will also affect brake light operation if defective

On most models the brake light circuit runs thru the turn signal switch. The third brake light does not. So it could be a problem with the turn signal switch.
A ground problem would also affect the parking lights.

Some year models have a electric lock on the brake pedal lever under the dash. Usually you can check it by pressing the brake pedal and observing the brake lights. If you lose this signal, the shift lever will not move from Park.

There can also be a shift rod inside the steering column which is linked to the ignition key. The shift rod can also be affected by the brake pedal switch failing to release the selector from Park. All 3 parts, ignition shift rod, brake pedal switch, and transmission release are adjusted together. Meaning if 1 does not work, the other 2 can be affected.

check brake transmission shift interlock fuse BTSI. check the NSBU fuse.which is the transmission neutral switch.if all is good check brake light switch.make sure brake lights working if not check fuse.when you apply brake that will energize brake transmission shift interlock solenoid.so you can shift out of park.if brake light switch is okay and fuse good.the brake transmission shift shift interlock solenoid could be faulty.

The brake light recall you got in the mail should fix the ESC light.

HYUNDAI IS RECALLING 532,633 MY 2006-2007 ACCENT, ENTOURAGE, SONATA, MY 2007 AZERA, ELANTRA AND SANTA FE, MY 2005-2007 TUCSON AND MY 2007-2008 VERACRUZ VEHICLES. THE STOP LAMP SWITCH IN THE AFFECTED VEHICLES MAY MALFUNCTION. A MALFUNCTIONING STOP LAMP SWITCH MAY CAUSE THE BRAKE LIGHTS TO NOT ILLUMINATE WHEN THE BRAKE PEDAL IS DEPRESSED OR MAY CAUSE THE BRAKE LIGHTS TO REMAIN ILLUMINATED WHEN THE BRAKE PEDAL IS RELEASED. A STOP LAMP SWITCH MALFUNCTION MAY ALSO AFFECT THE OPERATION OF THE BRAKE-TRANSMISSION SHIFT INTERLOCK FEATURE SO THE TRANSMISSION SHIFTER WOULD NOT BE ABLE TO BE SHIFTED OUT OF THE PARK POSITION. IT MAY ALSO CAUSE THE ELECTRONIC STABILITY CONTROL (ESC) MALFUNCTION LIGHT TO ILLUMINATE, AND IT MAY NOT DEACTIVATE THE CRUISE CONTROL WHEN THE BRAKE PEDAL IS DEPRESSED.

The stop lamp switch is used to judge if the acceleration system is abnormal. The stop lamp switch contains two switches monitored by the PCM. This is all covered at the dealer.

The stop lamp switch contains two switches monitored by the PCM. This will cause the issue you are having. It will illuminate the engine light also and cause the transmission to go into limp mode which is what's happening. Have replaced many for this same exact issue. This is what needs to be done next. The engine and ESC light come on together.

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CHECK BRAKE LIGHTS FUSE.IF FUSE OKAY.BRAKE LIGHT SWITCH IS BAD.VECHICLE NOT SHIFTING OUT OF PARK PROBLEM COULD BE BLOWED FUSE OR CLUTCH PEDAL SWITCH FOR MANUAL TRANSMISSION OR TRANSMISSION RANGE SENSOR FAULTY AND PROBLEM IN BRAKE LIGHT SWITCH IF FAULTY IT WILL KEEP THE BRAKE TRANSMISSION SHIFT INTERLOCK SOLENOID FROM WORKING KEEPING YOU FROM GETTING VECHICLE OUT OF PARK.IF BRAKE SWITCH IS GOOD.PROBLEM IN THE BRAKE TRANSMISSION SHIFT INTERLOCK SOLENOID.

I had this exact same problem...turns out it has to do with a recall having to do with the stop lamp switch. I took it to the dealership and it only took about 20 minutes form them to fix it.
Hyundai is recalling 531,894 MY 2006-2007 Accent, Entourage, Sonata, MY 2007 Azera, Elantra and Santa FE, MY 2005-2007 Tucson and MY 2007-2008 Veracruz vehicles. The stop lamp switch in the affected vehicles may malfunction. A malfunctioning stop lamp switch may cause the brake lights to not illuminate when the brake pedal is depressed or may cause the brake lights to remain illuminated when the brake pedal is released. A stop lamp switch malfunction may also affect the operation of the brake-transmission shift interlock feature so the transmission shifter would not be able to be shifted out of the park position. It may also cause the electronic stability control (ESC) malfunction light to illuminate, and it may not deactivate the cruise control when the brake pedal is depressed. Any of these malfunctions, alone or in combination, may lead to a crash. Dealers will replace the stop lamp switch free of charge. The recall began on April 23, 2009. Owners may contact the Hyundai Customer Assistance Center at 1-800-633-5151. This recall was the result of a Preliminary Evaluation conducted by the Office of Defects Investigation.

Did you check or replace the brake light bulbs?
It is more common to have burnt bulbs than a bad brake light switch or blown fuse.
Do you have orange signal lights and red brake lights at the rear?
Then the signal light switch will not affect the brake lights.....but....
If they are all red and you use the same bulbs for brake and signal....the brake light wiring goes through the signal light switch and could be affected there.
First....check for power getting to the brake light switch......and leaving it with a test light.......then go to the rear....pull a light assembly and check for power getting to the bulbs.no power? follow the wiring back to the switch looking for a bad connection.
The fuses and relays under the hood are usually in a black plastic box labeled fuses and or relays.

I had a problem with the interlock switch located on the brake pedal. There are too switches one for the brake lights and one dedicated to the cruise control. If either switch is acting up it will affect the cruise control. Then interlock switch is the same switch that is used on the clutch with cars that have a manual transmission. It has smaller electrical terminals in the connector than the brake light switch. You can jumper the connection and see if it solves the problem. You still have the other switch that will disengage the cruise control when you hit the brake. If that is the problem then that's the one you need to replace.