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Tail Light/Brake Lights Coming on Spontaneously??!?!
Hi Everyone.
I have a 2010 C300 4Matic w/ 77,xxx miles on it. Runs great but I seem to have a light problem. Randomly, the tail lights or brake lights will turn on, stay on for a few minutes, and then turn back off. It has happened numerous times. I did replace the headlight switch. I had a similar problem in another vehicle and the switch was the problem. I thought the issue went away after I replaced the switch. I did not see the lights come on for a while. At least I did not notice them come on at all. I searched the internet and found other types of similar issues but no posted solutions. I figure someone on here might have a similar problem. Any help is appreciated! Thank you!!
They come on when your driving, or when the car is off and parked?
If they come on when driving do you have the headlights on or off?
I would use a mercedes specific obd scanner to check for fault codes. Should lead you in the right direction.
If its the brake lights coming on/off it may be a faulty brake light switch. Part# 100 in the diagram. Try cleaning the connection maybe.
Check inside the front SAM for any signs of water getting in. I believe your exterior lights and brake lights are controlled from in there, at least the fuses anyways. I dont think the fuses are blown since they do work.
Hi Tim. I should have stated this before. The lights come on when the car is off and parked. I will just look outside and see them on. I will also stand by and watch them turn on and off..
is it just one side that lights up in the rear, the passenger side? Does the front parking light also come on when the rear light is on?
if so mine does that also. My light switch has left and right parking lights, they come on when you are parked and the car is off. there is something wrong where the parking lights randomly come on. The solution is to keep the light switch in auto mode.
It is both of the lights (driver and passenger side). I don't believe the front lights come on. I will have to look next time. My light switch also has the left and right individual park light mode. Not sure what that's is for. I usually leave it in auto mode. I took it out of auto mode to see if that would change anything.
You dont mention the 3rd brake light coming on so not sure its a faulty brake light switch.
Im guessing the rear parking lights are coming on, not the brake lights. Wonder if the front parking lights are also coming on, or even the fog lights?
I have been monitoring the car the past 2 weeks. You are correct. The third brake light does not come on and neither do the front marking lights. I believe it is just the two rear parking lights that are turning on and off. This is both with the light switch in Automatic mode and completely off.
Ok. I have continued to monitor the car for the past week. Yes, the third brake light does work properly ( as do all the other lights that I can see). When the lights turn on, it is all 4 bulbs on both the driver and passenger side of the vehicle. It is only the rear tail lights that I have seen turn on, not the front.
I have noticed that this issue doesn’t happen every time the car is off. Sometimes they never turn on. I have watched and checked regularly and found some days the lights are fine. However, when it does happen, the lights will turn on for about 4 minutes and then off for about 1 minute and the cycle continues until I disconnect the battery. I have installed a quick disconnect for the negative terminal so I don’t have to worry about the battery dying anymore.
Was it the brake light switch under the pedal? Or the headlight switch? I’ve already replaced the headlight switch and I thought that fix the problem. Unfortunately, it came back.
Curious if the license plate lights are also coming on?
Did you replace the headlight switch with a new or used switch? And is it a Mercedes switch or aftermarket?
Can you scan the car with a Mercedes specific obd reader? May tell you if you have a fault somewhere.
Im thinking either faulty light switch, or maybe an issue at the rear sam like water damage. Inspect the rear sam for any signs of water getting on it. The trunk trim has an issue with water leaking in at the fasteners and will leak right on the sam. I replaced all the fasteners in mine due to water getting in the trunk. Pull up the floor in the trunk and see if theres any water collecting on the floor below the spare tire.
Sorry, I didn't see you responded until yesterday. My bad.
I have not noticed the license plate lights come on.
I replaced the switch with a NEW OEM Headlight switch from Mercedes. I have been wondering if it is the switch and something caused this new switch to go bad as well. I will take a look at the rear SAM this weekend and see if it looks like there has been any water damage.
Initially, the new switched worked. That is why I am wondering if something caused this switch to go bad as well.
Rear sam is in the trunk behind the little door on the right side. Dont have to remove the entire panel to get to it, I just posted the photo to show it. Open the door and look all around with a flashlight for signs of water. In my searching for cause of tail light issues I came across a few where water leaking on the sam and caused some issues. The rubber on the trunk trim fasteners wear resulting in water getting thru, the sam is right below one of these fasteners. Can also check to see if water is getting in the trunk by removing the trunk floor and looking under the spare tire to see if there is any water collecting. My trunk trim was leaking and water was pooling under the spare tire. I replaced all the trim fasteners with new ones i picked up on eBay and so far it seemed to stop the leaks.
As far as the switch I really have no idea. I would think the front lights would come on also if it were the switch.
[QUOTE=TimC300;8988516]Rear sam is in the trunk behind the little door on the right side. Dont have to remove the entire panel to get to it, I just posted the photo to show it. Open the door and look all around with a flashlight for signs of water. In my searching for cause of tail light issues I came across a few where water leaking on the sam and caused some issues. The rubber on the trunk trim fasteners wear resulting in water getting thru, the sam is right below one of these fasteners. Can also check to see if water is getting in the trunk by removing the trunk floor and looking under the spare tire to see if there is any water collecting. My trunk trim was leaking and water was pooling under the spare tire. I replaced all the trim fasteners with new ones i picked up on eBay and so far it seemed to stop the leaks.
As far as the switch I really have no idea. I would think the front lights would come on also if it were
My car has done something very similar. Bottom of the passenger side rear lamp is ON while the front foglamp is on. It has happen with the headlamp switch on AUTO or on OFF.
If the switch is in park lamps, lamps are ON in the same manner.
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Was the issue solved?
