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2008 E350 4Matic Estate
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159 Posts
Discussion Starter #1
I replaced my brake switch last winter, hoping it would fix my cruise control issues (won't work/disengages after you've been driving 5-10 min).

It did not.

BUT, I made a silly mistake when installing the new switch; playing around to see how it worked, I changed the 'setting' of the old switch's plunger before adjusting the plunger on my new switch (I forget if I pulled it a few notches and/or pushed it in).

So I don't really know if the new switch is working properly, as I don't know if the plunger length is correct. Is there a way to determine if it's 'doing its thing' properly? I honestly don't really know what it does; does it actually activate the rear brake light? More stuff than that?

Is there any chance this issue could be affecting my cruise control? If so, do I want to remove & adjust the plunger of the switch...and if so, do I push it in 1-2 notches, or pull it out that many?

Thanks!
 

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2001 E430 4matic
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419 Posts
you have to take the brake light switch out and pull the plunger out all the way, when you install it, it adjusts automatically to the size needed to function correctly.
 

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1999 E300 TD
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46 Posts
The switch does adjust itself but you don't have to take it back out.
Just press the brake pedal and pull out on the plunger, then release the pedal slowly and it wil push the plunger in to where it needs to be.

The brake switch will interupt the cruise control but if it works for a while and then quits I would look for a failing relay or something like that.

-TDP
 

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2008 E350 4Matic Estate
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159 Posts
Discussion Starter #4
Thanks!!

Where is this relay you speak of? I'm dying to fix this...it really limits my to taking my old van when I go on long trips.

The switch does adjust itself but you don't have to take it back out.
Just press the brake pedal and pull out on the plunger, then release the pedal slowly and it wil push the plunger in to where it needs to be.

The brake switch will interupt the cruise control but if it works for a while and then quits I would look for a failing relay or something like that.

-TDP
 

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Registered
1999 E300 TD
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46 Posts
Thanks!!

Where is this relay you speak of? I'm dying to fix this...it really limits my to taking my old van when I go on long trips.
I didn't have time today but it was in the back of my mind to pull up a wiring diagram, I'll do my best to remeber to get one tomorrow.

I don't remeber exactly how the system works and it can vary from year to year but if you post the exact model and production date that will help me find the right stuff.

-TDP
 

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2001 MB E320
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37 Posts
Just got replacing my brake light switch. The Mech at the shop told me to use a 1.2mm feeler gauge between the plunger and the plate. The included directions said the same thing.
 
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