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E34 (1989 - 1995)

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  #1  
Old 09-24-2016, 07:14 PM
Vinnie D's Avatar
Vinnie D Vinnie D is offline
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Bad Brake Light Switch

Hi fellows,



Today my fairly new brake light switch (bought just a couple of months ago) failed on me while driving 15 min. away. My "Brake Circuit LT" warning light has been kicking in every day at some point after starting to drive. I wasn't really sure why. My brake pedal was touching the brake switch and brake lights were going on and off normally as they should.





Today at some point into my drive, I started to smell burning, but a quite different scent. Not the regular plastic burning or wire burn. I thought it had to do with my ventilation system, since somebody here had a problem and an old link was brought up where this guy's E34 caught on fire. I was pretty tense. I turned my fan off and pulled over. No smell in my engine bay. The bit of smoke was coming from under my steering wheel.



I made it to my destination and hours later came back home. Decided to investigate right away(It was night already), and found out that my brake light switch had partially melted and functionally destroyed.



The brand of it was MTC. I ordered a new one by FEBI, which it's supposed to be a reputable brand?!



I wont have the switch until Tuesday, and that is with Next Day Delivery. Hopefully I wont have any legal problems while driving without brake lights.



Just wanted to share it and suggest using better suppliers for such part.

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Last edited by Vinnie D; 09-24-2016 at 07:15 PM.
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  #2  
Old 09-24-2016, 09:35 PM
BMW_507_4ME BMW_507_4ME is offline
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Thanks

Quote:
Originally Posted by Vinnie D View Post
Hi fellows,



Today my fairly new brake light switch (bought just a couple of months ago) failed on me while driving 15 min. away. My "Brake Circuit LT" warning light has been kicking in every day at some point after starting to drive. I wasn't really sure why. My brake pedal was touching the brake switch and brake lights were going on and off normally as they should.



at some point into my drive, I started to smell burning, but a quite different scent. Not the regular plastic burning or wire burn. I thought it had to do with my ventilation system, since somebody here had a problem and an old link was brought up where this guy's E34 caught on fire. I was pretty tense. I turned my fan off and pulled over. No smell in my engine bay. The bit of smoke was coming from under my steering wheel.



I made it to my destination and hours later came back home. Decided to investigate right away(It was night already), and found out that my brake light switch had partially melted and functionally destroyed.



The brand of it was MTC. I ordered a new one by FEBI, which it's supposed to be a reputable brand?!



I wont have the switch until Tuesday, and that is with Next Day Delivery. Hopefully I wont have any legal problems while driving without brake lights.



Just wanted to share it and suggest using better suppliers for such part.

Attachment 577225
Attachment 577226
Thanks, but it sounds like you have a problem beyond a cheap switch? If the old one failed and the new one failed right after installing it, looks like some where there is a short or at least a high amp draw on your break light circuit, good luck with your car
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  #3  
Old 09-24-2016, 09:49 PM
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Vinnie D Vinnie D is offline
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The old one broke when I was doing my brake booster. So it was damaged while I tried to remove it and that's why I replaced it. Not sure about the new one.

What problem could that be, high amp
fuse?!
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  #4  
Old 09-25-2016, 01:49 PM
BMW_507_4ME BMW_507_4ME is offline
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Wire

Quote:
Originally Posted by Vinnie D View Post
The old one broke when I was doing my brake booster. So it was damaged while I tried to remove it and that's why I replaced it. Not sure about the new one.

What problem could that be, high amp
fuse?!
Wires can some times chafe and cause a high pull to ground or each other. A direct short should blow the fuse if you had that so I would "guess" something just increasing the resistance at the switch. I is unlikely even a cheap switch would melt from a normal amp pull in that circuit IMO What amp fuse do you have in there now?
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  #5  
Old 09-25-2016, 02:05 PM
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Vinnie D Vinnie D is offline
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I understand what you're saying.
I currently have a 15amp fuse in there, which is what the diagram says I has to be there.
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  #6  
Old 09-25-2016, 05:13 PM
BMW_507_4ME BMW_507_4ME is offline
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Amp

Quote:
Originally Posted by Vinnie D View Post
I understand what you're saying.
I currently have a 15amp fuse in there, which is what the diagram says I has to be there.
That is the correct fuse IMO. 15amps should not melt the cheap switch without blowing the fuse? the new switch MAY solve your problem, but I would test the amp pull at the switch plug in before I just hoped it will. If you do have a problem, a better made switch will just increase the chance of real problem with grounding or shorting somewhere in the car. I have not had that exact came problem in my car, so I will defer to any members that might have.
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  #7  
Old 09-25-2016, 05:41 PM
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Quote:
Originally Posted by BMW_507_4ME View Post
That is the correct fuse IMO. 15amps should not melt the cheap switch without blowing the fuse? the new switch MAY solve your problem, but I would test the amp pull at the switch plug in before I just hoped it will. If you do have a problem, a better made switch will just increase the chance of real problem with grounding or shorting somewhere in the car. I have not had that exact came problem in my car, so I will defer to any members that might have.
Do I only find out if the fuse is blown by using my meter or it will visibly show signs of being blown? Visually, it looks brand new.

How do I test the switch plug?

You are right that there could be problems that involves something other or but the switch itself, but in the meantime, the previous switch was fine, until I accidently damaged it myself and had to put this last one. I never had the "brake Circuit LT" sign until I put this replacement switch.
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  #8  
Old 09-27-2016, 05:00 PM
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TheEinstein TheEinstein is offline
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Have a good look at the wiring to the connector. As mentioned it could be a nicked wire up high if you weren't being too careful. As for testing the rest of the wiring, my suggestion would be to use an amp meter or circuit test lamp (looks like a small pen sized deal with a small bulb in it and a couple test leads coming out), to jump the connector pins. Ideally a digital amp meter that carries 10 amps should give a better idea of what the draw actually is per side.

Thing is, IMO, if it was a current draw issue, due to a short, I'd kind of expect some melted wiring near the switch too. Given only the switch seems to have suffered, my next phone call would be to whomever supplied that switch. Tell them the switch malfunctioned somehow and was stopped just short of starting your car on fire. Refund and some store credit please... They should want that switch back at their expense for investigative reasons if they're smart.
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1995 E34 540ia
160,000 Miles
VIN# ...GF32404
Hellrot Red

Fuelly

My Basic Repair History (Edited 1/27/2015)

Ongoing comparison between two E34 540ia's

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Last edited by TheEinstein; 09-27-2016 at 07:23 PM. Reason: Spelling... stupid tablet typing
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  #9  
Old 09-27-2016, 05:18 PM
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I contacted ECStuning and they refunded me. the new switch came in and it's replaced.

I did not find any other burned or melted wiring, not even by the plug.

I drove it to work and so far no warnings, but I will try to test the plug with a meter to see what I see.
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  #10  
Old 09-27-2016, 08:11 PM
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I tested the plug amperage and it was showing 13.1...does is sound right?
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  #11  
Old 09-27-2016, 08:48 PM
BMW_507_4ME BMW_507_4ME is offline
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Test

Quote:
Originally Posted by Vinnie D View Post
I tested the plug amperage and it was showing 13.1...does is sound right?
You might test at the fuse connections (remove the fuse and test at the contacts) and see if there is ANY amp pull with the switch disengaged, any pull could mean a short of some kind.

The good news is it has been working fine with the new switch. A easy test would be to hold the brake on for several min. while felling the wires that you can get to were you did the 1st repair that damaged the OEM switch. I don't know what happened that damaged the OEM switch and if some wires got stressed when that happened, but I would suspect that if there is a problem now that wasn't there before you damaged the 1st switch, they are related and should be in the same proximity.

If you smell ANY burning plastic (very easy to tell when you smell it) Release the brake and don't reapply till you find the burning insulation Please understand it is difficult to diagnose electrical problems even when you have the car right in front you, much less over the internet, good luck with your car
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  #12  
Old 09-28-2016, 09:05 AM
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TheEinstein TheEinstein is offline
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Given the 15A fuse, I'd say it's where it should be. BTW, and I realize it's pretty much self adjusting, but did you make sure it's adjusting correctly? IOW, do the brake lights come on with the slightest touch? A piece of printer paper slid in between the center brake light and glass will give enough reflection to see when the circuit closes, and that it doesn't hang on.

If you wanna get creative, bust an old bulb, take a file to any sharp glass left behind, cleanly separate the two pins that held the filament, insert the bulb into one socket at a time (no other bulbs in place), and verify each brake light location is getting the same voltage your battery is currently sitting at. I would expect a drop in voltage if there is a short somewhere.

You could even forgo the busted bulb thing, by removing all brake lamps/bulbs, and one at a time taking an amperage measurement (where you measured from before or at fuse location) for each particular socket/location. Should be able to effectively rule out any wiring issues, or at least have a pretty solid sense of all being well if all is equal.

I would mention though, I replaced my switch a while back when I started having the "Brake Circuit" message come up more and more frequently. I'd obviously tested all sockets, and replaced working bulbs just to be sure. Read here, that the switch was likely an issue, so I went to take it out. Not knowing how the smell the little clips worked on it, I busted one of the tabs that held it in place. So once I'd replaced it, I dissected it and noticed how the internals looked like they got pretty hot in the past. I'll see if I still have mine, as the metal internal to the switch was discolored from heat.

My suspicion is, once the contacts get enough carbon left on them, the resistance builds, and then excess heat results. I wouldn't be surprised for that switch, if made cheaply enough, to have done that on it's own. Just a thought
__________________
1995 E34 540ia
160,000 Miles
VIN# ...GF32404
Hellrot Red

Fuelly

My Basic Repair History (Edited 1/27/2015)

Ongoing comparison between two E34 540ia's

OBC4 Hidden Functions : Link
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  #13  
Old 09-28-2016, 09:53 AM
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Thank you sir!

So, they lights are working good, and they were with the burned switch as well.

Last night I just stepped on the brake a few times while having the door open and sticking out my head to look back there, I could see the light coming on and off and I played with the pedal.

What happened with the switch prior to the melted one, was that the little clip that holds the moving nipple broke, so the switch couldn't clip on to the metal frame thing, that is why I replaced it (sounds like what happened to you, Einstein), and before that, when I changed it for the very first time, I was getting the "Brake light switch" warning light..

I think it might have really being the cheap part I had put in...Everything else seems to be fine, and if you're saying that the amperage I could sounds normal, I guess I can keep my eyes on it (and nose too) and watch it.
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  #14  
Old 03-04-2017, 11:13 PM
E_Dirty_4_525i E_Dirty_4_525i is offline
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Where is this brake light circuit located? I've been getting that dash "brake light switch" warning light aswell.


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Old 03-05-2017, 12:45 AM
BMW_507_4ME BMW_507_4ME is offline
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Quote:
Originally Posted by Vinnie D View Post
Thank you sir!

So, they lights are working good, and they were with the burned switch as well.

Last night I just stepped on the brake a few times while having the door open and sticking out my head to look back there, I could see the light coming on and off and I played with the pedal.

What happened with the switch prior to the melted one, was that the little clip that holds the moving nipple broke, so the switch couldn't clip on to the metal frame thing, that is why I replaced it (sounds like what happened to you, Einstein), and before that, when I changed it for the very first time, I was getting the "Brake light switch" warning light..

I think it might have really being the cheap part I had put in...Everything else seems to be fine, and if you're saying that the amperage I could sounds normal, I guess I can keep my eyes on it (and nose too) and watch it.
I get a "brake light circuit" warning light on my 530i on and off all the time. I have tried to track it down, everything is working fine when it comes on, so I finally said WTH and just drive on
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Old 03-05-2017, 08:27 AM
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BMR_LVR BMR_LVR is offline
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Quote:
Originally Posted by BMW_507_4ME View Post
I get a "brake light circuit" warning light on my 530i on and off all the time. I have tried to track it down, everything is working fine when it comes on, so I finally said WTH and just drive on
Yeah, me too. My "brake light circuit" warning light is very intermittent. The brake lights have never failed to work when the warning is on so I just disregard it until it goes out again.
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It's Deja Poo - as in, I've heard this **** before.
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  #17  
Old 03-05-2017, 02:57 PM
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Quote:
Originally Posted by BMR_LVR View Post
Yeah, me too. My "brake light circuit" warning light is very intermittent. The brake lights have never failed to work when the warning is on so I just disregard it until it goes out again.
knock on wood, every since my last post, I put in a new (i believe it was a Febi brand) switch and the warning light has disappeared. I think the problem was the cheap switch I had in previously.
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Old 03-05-2017, 05:52 PM
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BMR_LVR BMR_LVR is offline
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Quote:
Originally Posted by Vinnie D View Post
knock on wood, every since my last post, I put in a new (i believe it was a Febi brand) switch and the warning light has disappeared. I think the problem was the cheap switch I had in previously.
The new switch no doubt fixed it , but unfortunately, it is likely just a matter of time before the warning comes back up. But, I hope you never have to see it again.
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Originally Posted by noego View Post
It's Deja Poo - as in, I've heard this **** before.
Steve

Calypso Red 1992 525i with 225K miles

1991 735i - Sold
1992 525i - Sold
1995 325is - Sold
2000 528i - Sold

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Old 03-05-2017, 07:03 PM
Mr._Graybeard Mr._Graybeard is offline
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Clean the brake light bulbs and contacts thoroughly. Make sure you have bulbs with "silver" metal housings rather than brass. The brass housings have been known to produce enough resistance to trip the brake light warning.
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Old 03-05-2017, 07:46 PM
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Originally Posted by Mr._Graybeard View Post
Clean the brake light bulbs and contacts thoroughly. Make sure you have bulbs with "silver" metal housings rather than brass. The brass housings have been known to produce enough resistance to trip the brake light warning.
Thanks for reminding me about that. I had forgotten about it. I'll have to take a look at mine sometime.
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Most problems are usually something simple !

Quote:
Originally Posted by noego View Post
It's Deja Poo - as in, I've heard this **** before.
Steve

Calypso Red 1992 525i with 225K miles

1991 735i - Sold
1992 525i - Sold
1995 325is - Sold
2000 528i - Sold

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  #21  
Old 03-06-2017, 05:45 PM
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Quote:
Originally Posted by Mr._Graybeard View Post
Clean the brake light bulbs and contacts thoroughly. Make sure you have bulbs with "silver" metal housings rather than brass. The brass housings have been known to produce enough resistance to trip the brake light warning.
Could you send me a link to those by chance, Mr. G?
Thank you sir.
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Old 03-07-2017, 06:20 AM
E_Dirty_4_525i E_Dirty_4_525i is offline
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I switched out the brake light switch and that wasn't the issue. Still have the two turn signals on and the brake light circuit. Any ideas or help on this and on how to fix it? Thanks guys


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  #23  
Old 03-07-2017, 08:08 AM
Mr._Graybeard Mr._Graybeard is offline
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Quote:
Originally Posted by Vinnie D View Post
Could you send me a link to those by chance, Mr. G?
Thank you sir.
You want No. 7506 bulbs. The more common 1156 bulbs will work, but they often have brass housings. Also, the wattage is different.
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Old 03-07-2017, 08:10 AM
Mr._Graybeard Mr._Graybeard is offline
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Quote:
Originally Posted by E_Dirty_4_525i View Post
I switched out the brake light switch and that wasn't the issue. Still have the two turn signals on and the brake light circuit. Any ideas or help on this and on how to fix it? Thanks guys


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Can you explain the problem more thoroughly? Your turn signal lights come on with your brake lights?
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Old 03-07-2017, 05:50 PM
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Vinnie D Vinnie D is offline
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Thank you Mr. G! I'll look that up!
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