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Discussion Starter #1
hello all ive scoured the forum for days and im getting desperate.

i have a 2000 ML430 92k

the brake lights do not work including the center light on the back window

left right signals work
hazard works
(lowest light on the tail light, when you turn on the headlights)works

i was so excited to see the stop light switch work for so many people i was sure this was going to fix my issue too but when i installed it today it did not work. i bought a OEM stop light switch from the dealer. i have swapped all bulbs to new, i have checked all the fuses and relays.

is there anything else anyone can suggest i look at?
also is there a wiring diagram somewhere?

im so lost right now any help is appreciated thank you forum members!
 

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Please update your profile in USER CP to include the year and model of your truck.

Go to the Stop Light Switch, with the truck running, and with a test light, test the GREY wire and see that you get voltage. If you do, then depress the brake pedal and at the same time test the BLUE wire and see that you get voltage. Report back with results.
 

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Discussion Starter #4
ok so i did the voltage test

gray wire yes voltage is present showing approx 14v

blue wire yes voltage when brakes pressed none when not pressed (or was it the opposite way around) either way yes both show voltage.

what does this tell me?

thank you
 

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Discussion Starter #5
oh one more thing.

which fuse and relay controls the brake lights, and stop light switch i want to be positive that i have checked the correct ones. these are the ones i have checked on

relay K6 (brake light suppressor/esp
relay k12 (brake light switch)
fuse F15 (brake lights/brake light switch

also do the relays tend to go bad?
 

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oh one more thing.

which fuse and relay controls the brake lights, and stop light switch i want to be positive that i have checked the correct ones. these are the ones i have checked on

relay K6 (brake light suppressor/esp
relay k12 (brake light switch)
fuse F15 (brake lights/brake light switch

also do the relays tend to go bad?
Check for voltage at f15 with brake pedal depressed.
 

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Discussion Starter #7
ok so at fuse 15 with the voltage meter with black stick on the ground (car) and red stick on the top of one end of the fuse i get a reading of .004 V (which fluctuates up and down a little bit) with the brakes pressed down. (let me know if im not using the meter correctly)

for what its worth i also tested with car completely off and not pressing on brakes it reads a .010V

also tested head lamps ON fuse 3 and fuse 5 both with a reading about .100
 

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The reason I suggested TEST LIGHT is because it is much easier to use in a confined area. I did not say volt meter, which obviously you don't know how to use.

If you are getting voltage at the blue wire, the next step is to check to see that you are getting current to BOTH contacts on the fuse. With the truck running, someone must assist you with depressing the brake pedal, while you check for current at the fuse.

1. If with the test light you get current at one contact on the fuse but not the other, the fuse is blown.
2. If you do not get current at either contact on the fuse, then the blue wire from the brake light switch to fuse #15 is broken.
3. If you get current at both contacts and the brake lights still do not work, then the ORANGE feed wire from fuse #15 to the brake lights is broken or corroded somewhere.
 

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Discussion Starter #9
yeah you are right that i dont know how to use this volt meter it was something that i had at work that i thought i could use, maybe ill pick up a test light

would you know where i can find out how this orange or blue wire is run throughout the car? like a diagram or something.

also does this said orange wire run to the 3 lights in line or do they split at some point?

thank for both of your responses it is very informative.
 

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Discussion Starter #10
so i got a light tester. again i tested at the stop light switch both grey and blue both with current.

went to test fuse 15 no current.

fuse itself is good.

so i guess at this point i will trace the blue wire see what i come up with. will be back with results.
 

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so i got a light tester. again i tested at the stop light switch both grey and blue both with current.

went to test fuse 15 no current.

fuse itself is good.

so i guess at this point i will trace the blue wire see what i come up with. will be back with results.
Did you check fuse #15 while the brake pedal was depressed?
 

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Discussion Starter #12
i traced the blue wire from the stop light switch all the way to underneath the fuse box it comes to a red square connector. when using the test light i do get current and it does go on and off as i press the brake pedal so i know it is the correct one.

is it possible the fuse box itself is bad?
 

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i traced the blue wire from the stop light switch all the way to underneath the fuse box it comes to a red square connector. when using the test light i do get current and it does go on and off as i press the brake pedal so i know it is the correct one.

is it possible the fuse box itself is bad?
It is possible but very uncommon. Pull out relay k6 and check at pin 3 if you get same signal. Rely is normally closed. From pin 4 signal continues to fuse 15.
 

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Discussion Starter #15
ok i removed the relay k6 at pin 3 i get current when brakes are pressed i get do not get current when brakes are not pressed. so it at that point it seems to be working.
 

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ok i removed the relay k6 at pin 3 i get current when brakes are pressed i get do not get current when brakes are not pressed. so it at that point it seems to be working.
Using two 6.3mm male connectors and piece of wire make a jumper. Bridge k6 pins 3 and 4. Check signal at fuse 15.
 

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You will find connectors like that at any auto parts store as part of Bubba kit. Along with few pieces of wire and crimping pliers.
 

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I am referring to numbers in wiring diagram (post #14). Relay you are pointing to on flaebay is "normally open" relay used for things like fuel pump, windows and such. Brake light suppression relay is "normally closed"
It should be marked 85/86 for relay electromagnetic coil and 30/87a for closed contacts.
 

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Discussion Starter #20
I am referring to numbers in wiring diagram (post #14). Relay you are pointing to on flaebay is "normally open" relay used for things like fuel pump, windows and such. Brake light suppression relay is "normally closed"
It should be marked 85/86 for relay electromagnetic coil and 30/87a for closed contacts.
if that is the case it is entirely possible that i could be using the wrong type of relay after all this.

i will return with results tomorrow.
 
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