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Brake Light Switch Replacement
 
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Pelican Technical Article:

Brake Light Switch Replacement

Steve Vernon

Time:

1 hour1 hr

Tab:

$12 to $30

Talent:

**

Tools:

Philips head screwdriver, 17mm wrench

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

Switch

Hot Tip:

Remove the front seat to give you more room

Performance Gain:

Working brake lights

Complementary Modification:

Check all your brake light bulbs

The brake light switch is a common failure item on the W123's as the vehicles age but it is easy and inexpensive to replace and great place to start with doing it yourself work. If you have checked you bulbs and wiring and determined that the switch is at fault this article will walk you through replacing it.

The switch is located under the driver's side dash by the brake pedal. It can get quit cramped under the dash so if you want a little more room to work please consider removing the front seat. Please see our article on seat removal if you need more assistance.

Over the years your car may have been serviced by multiple people including previous owners and this can lead to parts replaced with different size fasteners and hardware. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches. If something is different on your vehicle please let us know and share your info to help other users. If you have any questions or comments or even a different procedure you would like to share please leave it below and please leave your vehicle information.

Remove the five screws holding the under dash panel and remove the panel, please see our article on under dash panel removal for additional information if you need it.
Figure 1

Remove the five screws holding the under dash panel and remove the panel, please see our article on under dash panel removal for additional information if you need it.

The switch is mounted to a bracket in front of the brake pedal arm (red arrow).
Figure 2

The switch is mounted to a bracket in front of the brake pedal arm (red arrow). The end of the switch rests against the brake pedal arm.

Pull the electrical connection straight back and off the switch.
Figure 3

Pull the electrical connection straight back and off the switch.

There are two 17mm nuts on the switch that hold it in place on the mount (red arrows).
Figure 4

There are two 17mm nuts on the switch that hold it in place on the mount (red arrows). These nuts help position the end of the switch so that the plunger on the end of the switch is slightly compressed (enough so the brake lights do not activate) while the brake pedal is at rest.

Use a 17mm wrench and loosen the nut closest to the base of the switch first.
Figure 5

Use a 17mm wrench and loosen the nut closest to the base of the switch first. There is very little room to work and you will only be able to turn the wrench a quarter turn at a time. Once the rear nut is lose you should be able to hold the front nut with your hand and unscrew the switch with your other hand.

With the switch out of the mount you can see how the two nuts are used to hold the switch to the mounting plate and can be adjusted so the plunger is depressed while the brake arm is in a rested position.
Figure 6

With the switch out of the mount you can see how the two nuts are used to hold the switch to the mounting plate and can be adjusted so the plunger is depressed while the brake arm is in a rested position. You should install the new switch so that the brake lights activate as soon as the brake pedal is pressed. Installation is the reverse of removal.

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Page last updated: Sat 12/3/2016 03:06:16 AM