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Turbo_B5
12-29-2014, 06:52 PM
Got some major problems. I have NO brake lights. All 3 do not work. I did this: http://www.audizine.com/forum/showthread.php/190417-DIY-B5-A4-Additional-Brakelight-Mod Last night and everything was working. now shits not working. I switched back to old bulb holders. And checked the fuses. They all seem good.


Please help!

Murph_129
12-29-2014, 06:55 PM
Not a thing changed? It was working after you did the mod, put it all together, check again after it was all cleaned up and put together. Still worked. Went to bed, came out today without touching anything. No brake lights?

Turbo_B5
12-29-2014, 07:01 PM
I just left work and noticed i didnt have the 3rd light. Get home checked everything and everything looks fine.

Murph_129
12-29-2014, 07:02 PM
I just left work and noticed i didnt have the 3rd light. Get home checked everything and everything looks fine.

I'm sure you already looked, but what about the fuse?

Turbo_B5
12-29-2014, 07:03 PM
Yep I checked the fuse. I am about to take each one out to check again.

A4ski
12-29-2014, 07:05 PM
Just a hunch, but the brake lights are operated (usually) by a very small and sensitive switch. The contacts on this switch are very small, and not capable of handling much more of a load than initially designed for. Putting additional load on the switch can burn up the contacts like the filament of a fuse. Sometimes youll get lucky and the mod will last for years, other times, you burn it up immediately.

Murph_129
12-29-2014, 07:05 PM
What about checking for power across the fuse? (With brake pressed and not pressed)

//If no power across the fuse with the brake pressed, pretty good chance its what A4ski said [up]

Murph_129
12-29-2014, 07:25 PM
Just a hunch, but the brake lights are operated (usually) by a very small and sensitive switch. The contacts on this switch are very small, and not capable of handling much more of a load than initially designed for. Putting additional load on the switch can burn up the contacts like the filament of a fuse. Sometimes youll get lucky and the mod will last for years, other times, you burn it up immediately.

Walking a thin line though of having enough heat and energy to mess up contacts yet not blow the fuse. Idk, worth a shot

Turbo_B5
12-29-2014, 07:36 PM
What about checking for power across the fuse? (With brake pressed and not pressed)

//If no power across the fuse with the brake pressed, pretty good chance its what A4ski said [up]

There is no power going across the fuse. Going to order an aftermarket switch from local shop tomorrow

Murph_129
12-29-2014, 07:39 PM
There is no power going across the fuse. Going to order an aftermarket switch from local shop tomorrow

Well the next thing is check the contact switch that A4ski is referring to. Check if the contacts are bad, and if your unsure, take the wires that the "switch" is connecting and touch them together (or use a jumper) to connect them yourself. Then see if there is power across the fuse/your brake lights come on when you do that.

//Sorry, I overlooked the second part of your post about ordering the new one. Cool, if you could update us, I'd like to know what you find out after replacing it [up]

Turbo_B5
12-29-2014, 07:44 PM
Well the next thing is check the contact switch that A4ski is referring to. Check if the contacts are bad, and if your unsure, take the wires that the "switch" is connecting and touch them together (or use a jumper) to connect them yourself. Then see if there is power across the fuse/your brake lights come on when you do that.

//Sorry, I overlooked the second part of your post about ordering the new one. Cool, if you could update us, I'd like to know what you find out after replacing it [up]

Im going to go jump the wires and will report back

Turbo_B5
12-29-2014, 07:51 PM
I goto jump the switch is a 4 pin. What the fuck? ECS says 2 pin is for AEB. http://www.ecstuning.com/Audi-B5_A4-Quattro-1.8T/Search/SiteSearch/Brake_Light_Switch/

A4ski
12-29-2014, 07:52 PM
Got an ohm meter? Most $5 voltmeters have ohm reading capability. volts/ohms=amps. amps x volts = watts. You are sending 12 volts to those bulbs. Hypothetical example: If each bulb is 120 ohms, and there are 6 of them, then you are asking them to draw (12/120) x 6 = .6 amps. doesn't sound like much, BUT that = .6 x 12, which is 7.2 watts. If your switch is not rated at least 7.2 watts or .6 amps at 12 volts, you're gonna burn the switch. Do this for everything you are asking of that switch (resistance of your bl bulb over 12v x #of bulbs you are firing) and make sure your switch can handle it. It may handle it one day, and not the next, electricity does strange things. Conductors are temperature sensitive. Double redundancy is a good rule of thumb for DC electrical circuits.

Murph_129
12-29-2014, 07:54 PM
I goto jump the switch is a 4 pin. What the fuck? ECS says 2 pin is for AEB. http://www.ecstuning.com/Audi-B5_A4-Quattro-1.8T/Search/SiteSearch/Brake_Light_Switch/

Well the description of one of the switches that says a 4 pin says it sends signals elsewhere as well possibly ABS/ECU. One will be a solid 12V as your signal wire. And one goes off through your fuse and then to the relay (I'm assuming there is one for the brake lights? im not actually sure.) I'm trying to find a schematic now to see what all that whole circuit consists of. Gimme a minute and ill see if I can find that switch in the schematics.

//What's the color of your wires down there?

Murph_129
12-29-2014, 08:01 PM
One step in the right direction. The pins you need is Pin 4 which should be 12V and Pin 1 which should go off to your fuse and relay. Pin 4 is Red with a black stripe and Pin 1 is Red with a brown stripe

Murph_129
12-29-2014, 08:04 PM
Got an ohm meter? Most $5 voltmeters have ohm reading capability. volts/ohms=amps. amps x volts = watts. You are sending 12 volts to those bulbs. Hypothetical example: If each bulb is 120 ohms, and there are 6 of them, then you are asking them to draw (12/120) x 6 = .6 amps. doesn't sound like much, BUT that = .6 x 12, which is 7.2 watts. If your switch is not rated at least 7.2 watts or .6 amps at 12 volts, you're gonna burn the switch. Do this for everything you are asking of that switch (resistance of your bl bulb over 12v x #of bulbs you are firing) and make sure your switch can handle it. It may handle it one day, and not the next, electricity does strange things. Conductors are temperature sensitive. Double redundancy is a good rule of thumb for DC electrical circuits.

Just curious, any electrical background? [:d]

I'm a Junior this year going for Electrical Engineering Technology. Technical talk is an odd and welcome sight to see on here, but I know it isn't restricted to just people trained in it.. Just curious!

Turbo_B5
12-29-2014, 08:04 PM
http://c1552172.r72.cf0.rackcdn.com/267781_x800.jpg

http://c1552172.r72.cf0.rackcdn.com/313433_x800.jpg

Looking at the 2pin and the 4 pin. I should jump the big ones?

Murph_129
12-29-2014, 08:08 PM
http://c1552172.r72.cf0.rackcdn.com/267781_x800.jpg

http://c1552172.r72.cf0.rackcdn.com/313433_x800.jpg

Looking at the 2pin and the 4 pin. I should jump the big ones?


Looking at the switches itself I couldn't tell you. If the harness connections with the Larger female holes are the Red with a black stripe and Red with a brown stripe, then yes.

//From the form factor of that two pin connector compared to the four pin connector it looks like you could actually hook up the 2 pin to your 4 pin harness and it would still work. Also I guess I can tell by looking at the pictures of them. Yes, the larger pins are the ones you want to jump.

//Doesnt hurt to still verify and be double sure by checking wire colors

Turbo_B5
12-29-2014, 08:20 PM
One of the wires is red and yellow and other red and black. put a wire to jump them and nothing happened. Hopefully a new switch fixes my issue.

A4ski
12-29-2014, 08:22 PM
Just curious, any electrical background? [:d]

I'm a Junior this year going for Electrical Engineering Technology. Technical talk is an odd and welcome sight to see on here, but I know it isn't restricted to just people trained in it.. Just curious!

Quick self-bio: I am a design engineer for a company that builds pipe organs, all modern versions of which use 12v DC electrical control systems with literally thousands of solenoids. I have not seen it all, but I've seen a lot. Adding the extra brake light bulb is like putting 3 fat chicks in a canoe designed to hold 2 skinny ones. Sure, it might not sink, but one stiff breeze or ripple in the water, and it will. Electricity does odd things: ambient temperature and component manufacturing variations can make your diagnostic attempts seem to defy logic. Knowing the limits and sticking to them by a safe margin is the only sure thing. Put your brake lights back to normal, the switch under the pedal was made to handle the original number of bulbs, the ECU and ABS signal (which is likely next to nothing as far as current draw) and nothing more. Yes, the mod may work for years, but you may also have problems. You ARE having problems. ;)

Murph_129
12-29-2014, 08:31 PM
One of the wires is red and yellow and other red and black. put a wire to jump them and nothing happened. Hopefully a new switch fixes my issue.

Well sorry I couldn't help you in getting it resolved tonight. Let me know what develops from you connecting up the new switch (which I'm doubtful of since manually jumping them did not do it for you), but it's still worth a shot. Next up is to swap out your relay with another one of the same kind and see if that fixes it. Or look at the schematic on the side of the relay and jump the pins together at the relay if you can't replace it with another to test it. The coil could have somehow of been damaged in a similar fashion and the relay is just bad. Also testing to see if the positive side of the coil for the relay is even getting power.

Just some things to poke around at and test. I'd be more than glad to help you out with it when you get around to it.



Quick self-bio: I am a design engineer for a company that builds pipe organs, all modern versions of which use 12v DC electrical control systems with literally thousands of solenoids. I have not seen it all, but I've seen a lot. Adding the extra brake light bulb is like putting 3 fat chicks in a canoe designed to hold 2 skinny ones. Sure, it might not sink, but one stiff breeze or ripple in the water, and it will. Electricity does odd things: ambient temperature and component manufacturing variations can make your diagnostic attempts seem to defy logic. Knowing the limits and sticking to them by a safe margin is the only sure thing. Put your brake lights back to normal, the switch under the pedal was made to handle the original number of bulbs, the ECU and ABS signal (which is likely next to nothing as far as current draw) and nothing more. Yes, the mod may work for years, but you may also have problems. You ARE having problems. ;)

That's awesome! I'm going for EET but I'm also picking up a minor in CIT. Right now I'm doing a Co-op (Multi session Internship) with a compnay out of Detroit that does control systems and Error proofing systems for Ford Assembly plants. I leave for Kansas City in two weeks to stay for 3 months or so working at a plant there. Hoping to do some form of Industrial controls at a new GE plant near me once I graduate

Turbo_B5
12-29-2014, 09:16 PM
Well sorry I couldn't help you in getting it resolved tonight. Let me know what develops from you connecting up the new switch (which I'm doubtful of since manually jumping them did not do it for you), but it's still worth a shot. Next up is to swap out your relay with another one of the same kind and see if that fixes it. Or look at the schematic on the side of the relay and jump the pins together at the relay if you can't replace it with another to test it. The coil could have somehow of been damaged in a similar fashion and the relay is just bad. Also testing to see if the positive side of the coil for the relay is even getting power.

Just some things to poke around at and test. I'd be more than glad to help you out with it when you get around to it.


Thanks alot Murph and A4ski!

Murph_129
12-29-2014, 09:29 PM
Thanks alot Murph and A4ski!

Yea no problem man, just wanting to help out in any way I can! [up]

Turbo_B5
12-30-2014, 03:10 PM
Bought a new switch from the dealer @$32.03 (PN:4a0945515A) Hopefully will be here tomorrow or after the new year.

Murph_129
12-30-2014, 03:49 PM
Bought a new switch from the dealer @$32.03 (PN:4a0945515A) Hopefully will be here tomorrow or after the new year.

[up] Keep us posted

A4ski
12-31-2014, 03:18 PM
Yeah, I'm curious to see how this pans out. I thought of something else: I once lost all my brake lights (except the middle one on the trunk deck) on this POS Chevy monte carlo. Replaced the pedal switch, nada. Turns out it was in the turn signal switch, hence the middle bulb not being affected. My buddy's dad (a chevy dealer mechanic) figured it out by wiggling the turn signal switch while someone watched the lights. Audis might not work this way, but it's a possibility.

Turbo_B5
12-31-2014, 05:38 PM
Dissembled the switch.

http://i.imgur.com/2psnsCI.jpg

http://i.imgur.com/dIYlDxx.jpg

http://i.imgur.com/zTa6tL3.jpg

http://i.imgur.com/aLHZ6VX.jpg

seanf86
12-31-2014, 05:38 PM
Yeah, I'm curious to see how this pans out. I thought of something else: I once lost all my brake lights (except the middle one on the trunk deck) on this POS Chevy monte carlo. Replaced the pedal switch, nada. Turns out it was in the turn signal switch, hence the middle bulb not being affected. My buddy's dad (a chevy dealer mechanic) figured it out by wiggling the turn signal switch while someone watched the lights. Audis might not work this way, but it's a possibility.

they will if the turn signals and brake lights share the same bulb. Not sure about the 98+ cars with all red tails but I know the 97s have separate turn signal bulbs.

Murph_129
01-01-2015, 05:07 PM
Switch come in yet or still waitin'?

//Just really curious as to what the problem is

Turbo_B5
01-01-2015, 05:24 PM
I didn't get a call. But I have been at work all day so I wouldn't of been able to pick it up anyways. Hoping they will be here tomorrow. Will call them in the morning.

Also I am running facelift tails 1999.5+ Not prefacelift 1997- tails (check out my build thread below)

Thanks for being so eager to help. I am too. Really miss driving the car.

A4ski
01-01-2015, 05:35 PM
I see your switch has clear evidence of arcing between contacts. I've seen that alot on relays when someone is running too much current through them. The relay will usually weld its contacts together, but your brake pedal switch has a stronger return spring, so it just keeps burning the contact points until there is no more common conductive surface between them. Hence the working initially, followed by random failure. You need a bigger switch, or higher ohm bulbs.

Turbo_B5
01-02-2015, 10:17 AM
Picked up the new switch before work and will install it after work.

Murph_129
01-02-2015, 04:45 PM
Well? [up]

Turbo_B5
01-02-2015, 06:53 PM
Switch is in and still no fucking brakes. Couldn't get the vacuum switch back in. What is that for?

Where do I go from here?

Please help!

Murph_129
01-02-2015, 08:02 PM
What vacuum switch? Check your fuse again just to be sure. Next up is your relay. If that's fine. Then its possibly a power sourcing issue. You really need a multimeter man. Ground the negative probe and start poking around with the positive at your connections to ensure you in fact have voltage there. Gimme a second an I'll draw up a visual for our situation

Turbo_B5
01-02-2015, 08:22 PM
Where is the relay located and what is its number?

Murph_129
01-02-2015, 08:49 PM
//EDIT

Well I decided to remove my previous post because it appears I may have posted a lot of incorrect information regarding there being a separate relay for the brake lights. I don't want to waste your time and if I already have, I apologize, as soon as I get ahold of a schematic for a B5 and not a B6, I will continue to help you chase down this problem. For the time being. Take a meter and put your negative probe on a ground and take your positive probe to both sides of your fuse and ensure you have 12V at the fuse when the car is powered. From there, you can also check the pins at your brake light switch harness. The fuse and ONE of the LARGE pins on the brake light switch connector should have power no matter what if the car is on.

From doing a little searching, I see some people saying that the ABS module could be at fault as well preventing your lights from powering up, so if possible, scan for codes and see if anything comes up there.

Like I said, just probe the points where we know we should be seeing a voltage and when I get a full schematic we can continue in looking for other culprits.

Turbo_B5
01-04-2015, 11:21 AM
Went over the car at 2am last night and I fixed the lights! It was indeed a blown fuse. [headbang]

Murph_129
01-04-2015, 09:29 PM
Went over the car at 2am last night and I fixed the lights! It was indeed a blown fuse. [headbang]

at least its fixed now. [up]