Brake Lights Not Functioning - PeachParts Mercedes-Benz Forum

bbrewer · #1 12-02-2002, 11:32 PM

JUST when I think I've solved all of the problems, a new one pops up..... :-(
The brake lights don't come on when the brakes are applied....
I jumpered the connectors at the brake pedal switch in all the different combinations I could, but no luck there.
I seem to get a change in voltage across the fuse in the fuse box when I step on the brake pedal too.
Is there a connection somewhere, or another easy thing to test without taking apart every single brake component??

Any ideas??
It's a 1998 ML320 with 119k miles, and it is a recent occurence because it passed the state safety inspection about 3 weeks ago......

Thanks,

Barry

Gilly · #2 12-03-2002, 07:16 AM

2 of the contacts are normally open, the other 2 are normally closed. You may not have hit on the right combination. Usually a failure of this type will set the ESP/BAS light. Possibly it is a failure type I am not familiar with (No brake lights but no ESP warning light either).
My thought would still be a bad brake light switch as I have replaced quite a few. You could maybe check one of the brake light bulbs first to make sure for some odd reason they all failed at about the same time, or maybe the inspector did a bad job and never checked the lights. Check the center stop light bulb it's the easiest to get to.

Gilly

myarmar · #3 12-03-2002, 10:49 PM

On the switch:
1 - Green and 2 - White normally close
3 - Grey and 4 - Lt Brown normally open.

If the switch is OK, check fuse F15. This 10 Amp fuse is in the circuit for the all brake lights.

bbrewer · #4 12-03-2002, 11:27 PM

I "wish" it was something easy like that....... :-(

The switch tests out perfect with an ohmmeter, and the fuse is good, with no corrosion or anything like that.......

If I turn the ignition on, should I have power to one of those 4 wires at the switch connector??

Needless to say, it's NOT fun to be driving around, knowing people are not going to be seeing brake lights when you stop...... :-(

Thanks.

myarmar · #5 12-04-2002, 12:00 AM

Yes, with ignition ON you should have terminals 2 and 3 energized. When you push the brake, terminal 4 will get power. Then it goes to the relay K6 terminal 3 in the fuse box. Terminal 3 to 5 on this relay are normally closed, and then fuse 15 and all lights. Relay K6 is your next suspect I think. Terminals 1 and 2 - coil. Term 1 always hot. Terminal 2 being energized from the ESP system I believe to supress brake lights when ESP is working. Anyway, you need to check for continuity between terminals 3 - 5 on this relay.

bbrewer · #6 12-04-2002, 01:04 AM

Well...... here I am starting to get excited about the thought of tracking this down, and I learn that I don't "have" a K6 relay.... :-( I pulled the cover, see there wasn't even a relay IN the K6 slot, and I think I've solved my problem..... :-)
Then I double check the relay listing, and K6 is supposed to be empty........

I'll check power to the various wires at the switch tomorrow, but this is where I am at the moment.......

bbrewer · #7 12-05-2002, 12:21 AM

Well, I get power to the brake switch, and then switch completes the circuits when it is opened, and the reverse when it is closed.

There ARE a couple of loose plugs in the same area though, and I can't find what they might plug into, or even if it is related.

They are:
2 wire plug: orange & brown wires
4 wire plug: white/pink/orange/brown wires

And there is also a black "cable, about 15" long that is connected at one end right next to the brake light switch, and the other end is just dangling around down there. There is some kind of "tab" on the loose end that can be depressed and it springs back, but I have no idea what it does......

There must be a wire that runs from the switch to the rear of the vehicle. Anyone know what color that one is, and a easy place to check to see if it's getting power??

Thanks.

myarmar · #8 12-05-2002, 01:07 AM

The Light Brown wire from the switch pin 4 gets energized, then goes to the fuse box. You don't have K6 relay and I don't have diagramm for this. But if you have fuse F15, it gets there, then comes out of the fuse box as Orange wire. It goes to all brake lamps. Check if you're getting power on either end of F15 and from there to any brake light (with ignition ON and braking).
Good luck, Mike

Gilly · #9 12-05-2002, 08:42 AM

Just a quick question, have you checked any of the bulbs yet?

Gilly

bbrewer · #10 12-05-2002, 09:05 AM

Thanks for the circuit and wiring explanation.
I'll check into it further this weekend. (time is short right now)

I checked the center bulb. It was fine, and yes, you are certainly correct in it being the EASIEST to get to.... :-)

Thanks again.

bbrewer · #11 01-05-2003, 01:07 PM

Sorry to take so long getting back to this.......
But here's what I found:

There IS 12v getting TO the fuse when the brake pedal is depressed (with ignition on), so it seems that everything under the dash is working correctly.
The fuse is good, so it would appear that there is a break in the wire running between the rear of the vehicle and the first brake light that wire runs to.
Are there any wiring plugs or connectors for that orange wire that I can check first, and where are they located??

Thanks for working through this process with me. We ARE getting there.......

Barry

myarmar · #12 01-05-2003, 01:43 PM

Quote:

Originally posted by gillybenztech
Just a quick question, have you checked any of the bulbs yet?

Gilly

????

Gilly · #13 01-05-2003, 09:00 PM

Myarmar:
If you read through all the posts, no where does it say that he checked at least ONE of the bulbs (up to me directly asking the question).
Read my first post on this thread, the last paragraph.
Check the simple stuff first.

Gilly

bbrewer · #14 01-05-2003, 10:13 PM

Actually I did check the center bulb, and the circuit completed, and stated that in an earlier post.

In response to your post, I just now went ahead and REPLACED the center bulb, and the center brake light now comes on.
I double-checked the old bulb and it's out.
I must have crossed the wires (and yes, I DO feel stupid) :-( when I initially checked it with the ohmmeter.
Regardless, I then had one working brakelight.

After that, I went into the rear outer bulbs, and BOTH of those were burned out. I replaced them, and now have three working brakelights.

So, how do ALL THREE light bulbs ALL burn out at the same time??
Seriously, this just passed the state inspection one week before I noticed this, and I KNOW the bulbs were working because they would "light up" my garage when I back in at night.....
THAT'S the oddest thing.......

But anyway, thank you all for working through this "problem" with me.... Fortunately, I'm only "stupid" sometimes... (I hope) :-)

Barry

tabo · #15 01-05-2003, 10:33 PM

just change the bulb first before assuming its something else.. the bulb is less than $5, perhaps you drive like a maniac thats why your brake lights burn out so fast =PP in my honda accord if one brake light doesn't work, the instrumental cluster actually tells me, I don't think the ML has this option.. BUT the ML has the option when the brake pad is gone it will tell you, I think all cars should have this system... for safety reasons.