3rd Brake Light acting as running light?

Before anyone asks, YES, I did a search. I came up with tons of information on brake lights and even modifications or strange shorts, but nothing like this...

Two weeks ago, I got completely frustrated with blowing out bulbs in the Golf (at that point I only owned it for 3 weeks). So, I replaced the rear running lights and the brake lights with LED bulbs. I did not replace the flashers or the reverse lights due to how expensive the bulbs are (and I didn't want to mess with the flasher resistance issues on the relay). These things work great. They are slightly brighter than the incandescent bulbs, and they should last much longer with less energy consumption.

However, when I was backing into my garage last week, I noticed that I had a red reflection on my back wall when none of the lights should have been on. This is what I found...

The picture above is what my car looks like with the key in the ignition in the "ON" position (whether the car is running or not). The outer most bulbs on the 3rd brake light come on dimly when the ignition is on.
This remains true no matter if the running lights are on or not. Below is what the car looks like with the running lights on and the ignition in the "ON" position.

This "issue" does not seem to affect the function of the lights otherwise. Even the brake lights function normally.

This doesn't really bother me. As a matter of fact, I think its kinda cool looking. However, I would like the ability to disable this from happening.
Has anyone else come across this "issue"? Any ideas how to disable it?

It's probably a grounding problem.

-Jason

yup, it happened to my golf earlier this winter. I'll bet a six-pack that wires have cracked/chafed in the area where they exit body and enter the rear hatch, probably on the drivers side.
You have to remove the large plastic inner trim from the hatch to access the harness. Harness is all covered in a very sticky fabric tape.
Depending on where the breaks are you may be able to cut them out and connect wires back together with butt splices. IF you use butt splices make sure to buy ones with a heat shrinkable jacket to keep any moisture from findings it way into splice and causing resistance/corrosion.
In my case the brown ground wires where so stiff (insulation would crack every time wire was flexed) that I cut them back to a point inside the body and replace well into hatch harness. Doing this means taking apart drivers side inner cargo area liner and stick your arm up to harness in body from below to splice wires. Definetly helps to have someone manipulating wires/terminals from above while you are working blind from below.

While probably not great while driving, it'd be cool if you could get them to flash with your turn signal.

Well, since this car spent 4 years in the New Mexico desert and all the harsh heat and cold that goes with it, I wouldn't be surprised if several wires have hardened into crackling badly. I will be taking apart the rear of hatch and interior of the car this weekend to do some sound deadening and wire up some better cargo lights. I will look into those wires at that time...

Thanks for the responses! I will let you guys know what happens.

I will also end up looking at my driver's side door this weekend. The door switch will not register the open position...

Here comes the soldering gun.

Interestingly enough, I didn't attempt to fix this. I figured it wasn't harming anything. So, I left it alone. Turns out, when I put new pads on my rear brakes, the problem went away... The only explanation that I can come up with is that the brake pedal was sitting on the switch until the new pads were put in place causing the level in the reservoir on the master cylinder to rise thus causing the pedal to no longer sit on the switch. However, this is all speculation on my part.

The only explanation that I can come up with is that the brake pedal was sitting on the switch until the new pads were put in place causing the level in the reservoir on the master cylinder to rise thus causing the pedal to no longer sit on the switch. However, this is all speculation on my part.

Click to expand...

my 0.02
Respectfully, I'm pretty skeptical about that.

I can think of two possibilities: One being as the others have mentioned, a grounding problem, compromised wire etc. But another thing to keep in mind, have seen this with other cars before, not VW yet- If the car has an auto detect system that enables the computer to tell you when you have a bulb out, that system may keep the bulbs energized at a low level even when foot is off the brake etc. That wouldn't be enough to light a regular incandescent bulb, but the LED bulbs draw much less power (ie. they will light on much less power) and so you might be experiencing that- just the natural function of the car that's designed assuming the presence of regular filament bulbs. I know this can be an issue on Dodge trucks sometimes- people replace the original filament bulbs with new LED ones (which are indeed better in many ways). But the computer sees the lower current draw and thinks there's a problem with the bulb and starts telling the driver they have a burned out bulb. Of course, that doesn't explain if the issue went away after the brake job- that's back to a possible compromised ground somewhere, may have gotten disturbed. Bad grounds are usually more problem in the snow states that use (corrosive) salt on the roads in winter.

Wish you all the best.

Corsair said:

my 0.02
Respectfully, I'm pretty skeptical about that.

I can think of two possibilities: One being as the others have mentioned, a grounding problem, compromised wire etc. But another thing to keep in mind, have seen this with other cars before, not VW yet- If the car has an auto detect system that enables the computer to tell you when you have a bulb out, that system may keep the bulbs energized at a low level even when foot is off the brake etc. That wouldn't be enough to light a regular incandescent bulb, but the LED bulbs draw much less power (ie. they will light on much less power) and so you might be experiencing that- just the natural function of the car that's designed assuming the presence of regular filament bulbs. I know this can be an issue on Dodge trucks sometimes- people replace the original filament bulbs with new LED ones (which are indeed better in many ways). But the computer sees the lower current draw and thinks there's a problem with the bulb and starts telling the driver they have a burned out bulb. Of course, that doesn't explain if the issue went away after the brake job- that's back to a possible compromised ground somewhere, may have gotten disturbed. Bad grounds are usually more problem in the snow states that use (corrosive) salt on the roads in winter.

Wish you all the best.

Click to expand...

Thanks for the reply.

Yeah, this car spent many years in Northern New Mexico, Colorado, Kentucky, and North Carolina. So, corrosion is a problem on it. I am going to see what changes over time. If it continues to not be a problem, then I will consider myself lucky (for now).

I would like to update this thread because I had the identical problem and was taken aback by how simple it was (in my case) to fix.

My car is a 2003 GTI VR6, with no electrical mods and all stock, original lamps.

Like the OP, my high mount stop light would glow dimly at the outer ends, when the ignition was on and my lower stop lights were out.

When I would depress the brake pedal, the HMSL would come on normal, full bright and sometimes the lower brake lights would light, but more often they would not -- very dangerous! This did indicate however, that the lower stop lamps were not burned out. Upon switching off the ignition and pulling the key, the glowing HMSL would remain on and go out at exactly the same time that the interior lighting went out.

My V-Checker Pro showed the car was throwing Brake Electrical code "00526 Brake light switch F". So I replaced the brake light switch with the latest (1C0-945-511A-NAR, which I believe applies to all Mk4s). The new brake light switch did not alter the problem at all.

After some research, I considered replacing the HMSL (1J6-945-131C, which I believe applies to all Mk4 Golf types) and costs about $90.

I also considered taking out all of the rear trim and testing the wires through the hatch (where they flex) for shorts, but I wasn't looking forward to it.

The fact that the lower brake lamps would still sometimes light was leading me to believe that they were not the problem, but in fact they were the entire problem.

I was taught to always start with the simplest fix first, so before launching into the pricey and time consuming work, I put in some new lower brake lamps P21W (7506). Presto! Everything went back to normal and correct operation. I cleared the brake code 00526 and it has not returned.

Upon close examination, the 9-year-old lower brake lamps were found badly corroded inside, along the wires that hold the filament. I can still light them with a 9 volt battery, but they must have been causing some sort of grounding issue that allowed a small amount of current to dimly light the ends of the HMSL. I'm guessing the computer can only interpret this current flow as a bad brake light switch; code 00526.

At any rate, $4 worth of P21W lamps fixed the issue.

Anyone else have and resolve this issue? My 99.5 just started doing this.

03 Jetta Wagon TDI having the same issue with the 3rd brake light. Pulled the LED strip (through-mounted PCBA) and tested it with a 12V battery, works fine. Then checked the light's source voltage and it's only 10.4V, enough to dimly illuminate the outboard LEDs, yet throws the 16955 - Brake Switch (F) P0571 - 35-00 - Implausible Signal code.

Wiper spray hose elbow at the rear hatch had popped off and leaked fluid into the headliner and driver rear cargo corner. Currently undoing all the wiring loom (sticky fabric tape) and finding corroded connectors along the trunk floor. The positive lead (red wire w/ black stripe) for the brake light is in parallel with several more components in the circuit.. still working my way upstream to find the source of the voltage drop.

My 99 jetta is going this after throwing leds in the brake lights. Brakes work fine just the 3rd glows with the ignition on. Ill go through the wiring here in he next few days if the weather is nice. Might just be the leds are causing a short or something.

As I said earlier, it's from the cruise control safety cutoff... the ECU grounds itself through the brake lights, when the ground goes away it knows the lights are on and the pedal is pressed.

If you want to get rid of the glow add a resistor that dissipates ~5 watts to the brake light circuit.

moparvwfrak said:

My 99 jetta is going this after throwing leds in the brake lights. Brakes work fine just the 3rd glows with the ignition on. Ill go through the wiring here in he next few days if the weather is nice. Might just be the leds are causing a short or something.

Click to expand...

I had the glow plug light blink when I put in LED brake lights.
Had to install load resisters to stop it.
Wally World (AKA Wal-Mart) sells them also.
I didn't check the high mount.

Appeared to have resolved all my issues tonight. VW has a bit of a safety language built into the car. Simply put, my 03 TDI Jetta Wagon needed tail light and indicator bulbs replaced, due to corrosion and moisture.

When a tail light or indicator bulb is out, the car indicates with:
dim, partially lit 3rd brake light, and
glow plug coil error.

Brake Tail lights are dual filament bulbs (notice 2-contact lower connectors).
part number 7528 (LL) LL-long lasting

Indicator lights are single filament, standard bulbs.
part number 7506 (LL)

The passenger side taillight panel access is through the first-aid kit panel cover. Pull the cover off and put the first-aid kit aside. Reach towards the tail light and pop the two tabs away from the taillights and out comes the assembly with the bulbs arrangement.

To remove a bulb, push down and twist a quarter turn.
The lower connector is also a spring, and will push the bulb out.

On the Jetta Wagon, the driver's rear quarter panel interior corner comes out to reach the bulb array. The stamped steel, kickpanel entry plate to the rear cargo comes out first; pull from the lowest edge and away from the body to release. Be sure to tuck interior body panels below rear hatch weatherstripping; use a plastic, non marring lever to pry.

Manningbilt said:

03 Jetta Wagon TDI having the same issue with the 3rd brake light. Pulled the LED strip (through-mounted PCBA) and tested it with a 12V battery, works fine. Then checked the light's source voltage and it's only 10.4V, enough to dimly illuminate the outboard LEDs, yet throws the 16955 - Brake Switch (F) P0571 - 35-00 - Implausible Signal code.
Wiper spray hose elbow at the rear hatch had popped off and leaked fluid into the headliner and driver rear cargo corner. Currently undoing all the wiring loom (sticky fabric tape) and finding corroded connectors along the trunk floor. The positive lead (red wire w/ black stripe) for the brake light is in parallel with several more components in the circuit.. still working my way upstream to find the source of the voltage drop.

Click to expand...

moparvwfrak said:

My 99 jetta is going this after throwing leds in the brake lights. Brakes work fine just the 3rd glows with the ignition on. Ill go through the wiring here in he next few days if the weather is nice. Might just be the leds are causing a short or something.

Click to expand...

I switched my brake lights to leds and having the same issue. What did you ever find out with this.

I had to install load resistors to use the LED bulbs.
One on each side with the brake light.

Wally World (AKA Walmart) sells them.
Don't remember the price but it wasn't much.

I've also read someone installed higher resistance ones to use less power and they worked.