HowToRepairGuide.com: How to troubleshoot Brake lights on vehicle?

Brake lights is the indicator to warm the drivers,that your car will be slowing down or stopping.There are basically 3 brake lights.Two are located in the low rear side of car and third is at the upper level deck lid or roof line.This lights are controlled by a switch.This switch is basically called " Brake Light Switch".

The brake electrical system is controlled/protected by small fuse.If the brake lights stops working,then mostly the possibility is shorted fuse or faulty brake light switch.
Brake light switch is basically connected to brake pedal.The brake light switch circuit is in open position,when you depress the brake pedal,this circuit gets closed and brake lights gets illuminated.
This switch is easily adjustable by moving the main switch housing within the metal bracket that holds the switch. Not in all car models,but on some car models the brake light switches have additional functions such as the cruise control brake sensor and ignition key interlock function.

In some brake lights problem,the problem occurs due to brake lights itself.This brake lights burns the brake light bulb,if they are not turned off.If by case,the brake lights are not turned off then this melts the brake light holding sockets,as well as the brake light bulb.lens.

Repairing brake lights problem on American cars and Japanese/European cars are bit different.

On American cars ,the car makers have incorporated the brake light circuit into the turn signal system, and vice versa.But on Japanese and European cars,the makers design the brake and turn signal electrical systems separately. For this reason troubleshooting the same problem will be slightly different from the two different styles of manufacturing.
If you notice that your car brake lights are not working,then first inspect the brake light fuse,if the fuse gets faulty,it will not allow the electrical current to continue to the brake lights.The fuse is located in the fuse box.There are basically two fuse boxes in car.One under hood in engine compartment and another fuse box under dash,its called instrument panel fuse box.
The brake light fuse can be located in any of the fuse box ,depending on car models.
Once you locate the fuse,then test the fuse to confirm that fuse is a problem.To test the fuse you need a test light.The 12 volt testing,its easily available at local auto parts store.Now to test connect the test light to a ground like an engine or dash bracket .Then turn the ignition key to the "ON" position.Dont start the car,just turn ignition switch to ON position. Then with the test light probe both sides of the fuse. If the test light illuminates on both sides the fuse,then the fuse is okay.But if one side of the fuse illuminates then the fuse has failed and needs to be replaced.
Now if you replace the fuse,and it fails as soon as you start the car or apply the brake pedal,Then brake light electrical circuit is shorted to ground.The wiring to brake light switch needs to be inspected.Or you can disconnect brake light wiring from brake light bulb to brake light switch,and connect external wire from brake light bulb to brake light switch and check.

Another possibility for no brake lights can be faulty brake light bulb.In the bulb there is a thin metallic filament.If this filament gets short the bulb will not glow and you have no brake light,to that bulb.There are three brake light bulbs, basically,one or two bulbs gets faulty.All 3 bulb going faulty at once is rare,but still has to be confirmed.Remove the bulb and manually inspected.If the metallic filament is shorted,you can easily see in the bulb.In that replace that bulb.

If brake light fuse is checked ok,if brake light bulb or lens are checked good.Then other possibility for no brake lights working is faulty brake light switch.
To test the brake light switch,you need a 12 volt test light.Brake light switch has two wires.The switch is located near or the side of brake pedal.
Out of this 2 wires,one is power in and power out,power out connects to turn signal switch.
Use a test light that is grounded and then turn the ignition key to "ON" position.Then test for power at one side (wire) of the switch.Now press the brake pedal while testing the opposite side (wire). It should illuminate the test light, if electrical power is connected through the switch. If no power is detected through the switch the brake light switch has failed and replacement is required.

On some Japanese/European car models there is Brake light control module.If this module fails or stops working,then it can also cause no brake light working problem.
All cars dont have this module,But in cars where there is module,then this module is located near the rear seat of the drivers side.To test if module is faulty,test for incoming power to the brake light switch.
If incoming power is present without outgoing power replace the brake light control module with new to recheck system.

On some car models there is separate module to control the lights system of the car.This module is called BCM.BCM means Body Control Module.If you notice that all parts,that connects to brake lights are checked ok,then its quite obvious that BCM is malfunctioning and causing the problem.
Note BCM also controls the other light operation in car,and not ONLY the brake lights.In most cases BCM has to be scanned by car scan tool.If BCM scanning shows error codes,then that error code will point towards what is causing fault.But if no error codes are shown,then BCM is faulty and needs to be replaced.

Sometimes you notice,that brake lights are dull or they flickers.
In this case,its possible that brake light bulb is got weak,or if you have recently replaced the brake light bulb,then you have not bought correct brake light bulb.May low quality/ cheap after market bulbs are not supportive.They don't give correct results and starts getting dull or flickers.But if you are confirm that bulb is good and branded,then its possible that problem is short or loose wire somewhere.
Test it with test light to confirm this.
To test this turn the ignition key to the "ON" position.Then with the help of helper depress the brake pedal. With the bulb installed touch a grounded test light to the outer bulb holder ring. If the bulb brightness changes the bulb socket ground has high resistance and needs to be repaired or replaced.This test will let you confirm the problem.
Basically the bulb flickers when the power or ground is being obstructed momentarily.If th brake light bulb is fitted loose,then bulb will flicker,because its connection will get connected and disconnected,this results in flickering.Another possibility is loose brake light socket or loose brake light wiring or its wiring is not properly grounded,connect external ground for brake light bulb.

This basic tests and troubleshooting will help you to understand your car brake light system and its working.So you can confirm the problem.
Buying branded parts is always advisable.Low quality car parts are cheaper,but don't last long.High quality,original parts lasts,long and give good results.They are bit costly,but they are worth to buy.
This will help.
Thanks.
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