Brake lights on. New switch and grounded bulbs not the issue

Bret2094

Member
Joined
Jun 25, 2018
Location
College station, TX
TDI
1999.5 Jetta , 2002 Jetta,2003 Jetta Wagon, 2003 Jetta Wagon Non sunroof
Hi everyone,

I recently bought a 1999.5 TDI 5 speed Jetta that had a previous owner that was not kind to the wiring. Before I go any further I would like to state that I have used the search function, and exhausted the topics that are similar to my issue. When I bought this car, cruise control did not work properly, and there appeared to be a crummy repair to the brake light switch harness plug. Once I got home with it, I began to investigate and found that the red and black signal wire to the tail lights had been cut and a wire had been substituted and ran all the way directly to the brake light switch. For the sake of everything being correct, I got a section of wire from a junkyard, an spliced everything back I'm, and bought a new brakelight switch.

I have the following issues

Flashing glow plugs light
ABS light
Unable to turn on cruise control
Constant on brake lights

I have checked each bulb, meticulously cleaned and replaced, checked the switch, gutted the car from trunk to dash, and checked for shorted wires. Fuses have all been tested, and the codes have been cleared in vagcom. Brake fluid is topped off to full.

Unplugging the harness from the brake light switch does nothing,

Any thoughts?

Bret
 

mr.loops

Veteran Member
Joined
Nov 24, 2010
Location
Kelowna
TDI
2002 jetta, 2003 Bora 1.8T
You could have an internal short or corrosion in one or both brake plate socket trays

I would do a voltage drop test on both socket trays. Pay close attention to your ground side voltage readings


Sent from my iPhone using Tapatalk
 

wonneber

Top Post Dawg
Joined
Oct 12, 2011
Location
Monroe, NY, USA
TDI
2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
Unplugging the harness from the brake light switch does nothing,
A bad ground (mentioned already) could cause the lights to go on by back feeding power through the bulbs.
If the ground under the battery tray is bad then anything that grounds to the body is bad

Are the brake lights on with the key off?

If the brake lights are on and not the head lights then measure the voltage from the bulb ground (at the bulb) to the negative terminal on the battery.
I would not want to see more then a few tenths of a volt.
This is a voltage drop test.

Next with the brake switch disconnected measure there is 12 volts at the bulb pin inside the socket.
If there is you will have to trace the wire back to the front for a short possible from the interior light circuit.
 

Bret2094

Member
Joined
Jun 25, 2018
Location
College station, TX
TDI
1999.5 Jetta , 2002 Jetta,2003 Jetta Wagon, 2003 Jetta Wagon Non sunroof
You could have an internal short or corrosion in one or both brake plate socket trays

I would do a voltage drop test on both socket trays. Pay close attention to your ground side voltage readings


Sent from my iPhone using Tapatalk
I forgot to mention that I have a known good set that I have swapped out for testing purposes. With the new time change, I haven't had any time during the week to check everything out in the daylight. I plan on getting back to this Saturday. As for everyone else that posted, thanks for the questions. I don't have multi quotes down on here yet, but the brake lights do in fact stay on with the car off, and the key removed. The third brake light remains lit as well. I have replaced fuse 13.....

Thanks for sticking with me here


Bret
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
Brake lights on with ignition off is almost certainly a mis-connect somewhere.
For multi quotes right click on quote, select open in new tab and cut and paste from there.
 

wonneber

Top Post Dawg
Joined
Oct 12, 2011
Location
Monroe, NY, USA
TDI
2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
the brake lights do in fact stay on with the car off, and the key removed. The third brake light remains lit as well.
That's what I needed to know.

and there appeared to be a crummy repair to the brake light switch harness plug.

I got a section of wire from a junkyard, an spliced everything back I'm, and bought a new brake light switch.
I have the following issues
Flashing glow plugs light
ABS light
Unable to turn on cruise control
The issues just above are consistent with a brake light issue by design.

If you unplug the brake light switch there should not be any power going to the back brake lights.
Take fuse 13 out to see if the lights go out.

If not check if pin 1 (red/brn wire) of the socket has 12 volts to it. It shouldn't.

Check pin 4 (red/blk). There should not be power there. (fuse still out).
If there is that's where the problem is.
Look around in the back if someone jumped wires there. (long shot)
Is there a convenience outlet back there that's always hot?

I'm assuming you connected the correct color wires together with the J-Y switch.

Try pulling fuse 43 to see if they go out. Should be a 10 amp fuse.
 

Bret2094

Member
Joined
Jun 25, 2018
Location
College station, TX
TDI
1999.5 Jetta , 2002 Jetta,2003 Jetta Wagon, 2003 Jetta Wagon Non sunroof
That's what I needed to know.
The issues just above are consistent with a brake light issue by design.
If you unplug the brake light switch there should not be any power going to the back brake lights.
Take fuse 13 out to see if the lights go out.
If not check if pin 1 (red/brn wire) of the socket has 12 volts to it. It shouldn't.
Check pin 4 (red/blk). There should not be power there. (fuse still out).
If there is that's where the problem is.
Look around in the back if someone jumped wires there. (long shot)
Is there a convenience outlet back there that's always hot?
I'm assuming you connected the correct color wires together with the J-Y switch.
Try pulling fuse 43 to see if they go out. Should be a 10 amp fuse.
I tried all of this, with no luck, but I did do a voltage drop on the fuse panel one at a time. When I got to fuse 14, upon unplugging it, the brake lights went off and allowed me to use the brake lights normally, however the car will not start without it. Appears to be something in the interior lighting/central locking system that is shorting? I've got the interior out, but Jesus that looks like a ton of places to test. Currently looking around the forums for a solution. Any idea where to start ?

Thanks,

Bret
 

wonneber

Top Post Dawg
Joined
Oct 12, 2011
Location
Monroe, NY, USA
TDI
2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
I tried all of this, with no luck, but I did do a voltage drop on the fuse panel one at a time. When I got to fuse 14, upon unplugging it, the brake lights went off and allowed me to use the brake lights normally, however the car will not start without it. Appears to be something in the interior lighting/central locking system that is shorting? I've got the interior out, but Jesus that looks like a ton of places to test. Currently looking around the forums for a solution. Any idea where to start ?
Thanks,
Bret
Correct.
My fuse list (for a Jetta, not sure how different a Beetle is) indicates:
13. Brake tail lights (10A).
14. Interior lights, central locking system (10A).

Took a bit of searching but found fuse 14 is part of anti theft system.
Feeds: COMFORT SYSTEM CENTRAL CONTROL MODULE CENTRAL LOCKING & ANTI-THEFT WARNING SYSTEM ANTENNA CENTRAL LOCKING WARNING LIGHT DRIVER'S SIDE CENTRAL LOCKING LOCK UNIT (BEHIND LEFT SIDE OF DASH) (UNDER LEFT SIDE OF DASH) (BEHIND LEFT SIDE OF DASH)

This would explain why the car wouldn't start with the fuse out.
I can't think of any reason the module (above) should be able to power up the brake lights unless it's circuitry shorted to the brake light wire.

Did you check if pin 4 in the socket had power when it's removed from the brake light switch?
It's a red/blk wire, the same colors as the fuse 14 wire.

You mentioned that wire was cut and a new wire run to the rear.
Does that one have power all the time?
 

eddieleephd

Top Post Dawg
Joined
May 27, 2012
Location
Battle Ground, Wa
TDI
2002 jetta Wagon
Your lady post makes me think you have a faulty relay. The one that controls first 14 that when pulled makes the lights go out. Look into that circuit more and circuits that run off of it.
Look for shorts to ground from there.

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Bret2094

Member
Joined
Jun 25, 2018
Location
College station, TX
TDI
1999.5 Jetta , 2002 Jetta,2003 Jetta Wagon, 2003 Jetta Wagon Non sunroof
Did you check if pin 4 in the socket had power when it's removed from the brake light switch?
It's a red/blk wire, the same colors as the fuse 14 wire.
You mentioned that wire was cut and a new wire run to the rear.
Does that one have power all the time?
Yes it does. Reads 11.9 volts at all times, unless fuse 14 is removed. With 14 removed, you only get voltage when the pedal is pressed, as intended. Checked on the back of the fuse panel to see if something had obviously been tampered with, but I haven't had any luck in that department. Unplugging the blue connector on the comfort module has the same effect as removing the fuse on slot 14. So far I've come across some janky wiring for the radio that I removed/ repaired alongside a couple of frayed wires for the puddle lights, but nothing that seems to solve the issue


Bret
 

wonneber

Top Post Dawg
Joined
Oct 12, 2011
Location
Monroe, NY, USA
TDI
2014 Jetta Sportwagon,2003 Jetta 261K Sold but not forgotten
Try following the power wire to the rear to find where it's getting power.
From your 1st post:
'found that the red and black signal wire to the tail lights had been cut and a wire had been substituted and ran all the way directly to the brake light switch'

Maybe disconnect it at both ends. If the light goes out then follow the wire gets power from.
 

AndyBees

Top Post Dawg
Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
I'm not familiar with the 99.5, but assuming it is similar or the same as the later models, there are two other circuits involving the connector to the brake switch. Those two circuits are for the Cruise Control (normally closed). And, obviously, the brake side of the switch is normally open.

From what's been said, I do understand that the brake lights stay on even if the brake switch connector is unplugged. However, if someone has been dicking with those four wires, they were probably looking for a problem that wasn't there. Those four circuits need to be positively identified and repaired.
 

AndyBees

Top Post Dawg
Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
The connector will only plug one way. However, the circuits (wires) could be mixed-up. That's why I suggested that they be found and specifically identified.
 

Bret2094

Member
Joined
Jun 25, 2018
Location
College station, TX
TDI
1999.5 Jetta , 2002 Jetta,2003 Jetta Wagon, 2003 Jetta Wagon Non sunroof
Try following the power wire to the rear to find where it's getting power.
From your 1st post:
'found that the red and black signal wire to the tail lights had been cut and a wire had been substituted and ran all the way directly to the brake light switch'

Maybe disconnect it at both ends. If the light goes out then follow the wire gets power from.
I spent all of yesterday following the red/black wire from the most forward point I could, to the rear of the car's harness and found nothing of suspect. The wire itself begins at the brake switch, goes up into the harness , at some point makes it's way down to the harness that follows the driver side all the way to the back. I've honestly run out of time having this one disassembled and nonusable as a commuter. On a hunch, and in an effort to make this thing driveable, I cut the red/black wire at the brake light plug, and just after the hood release in an effort to redneck test to see if the problem was under the dash somewhere. Both ends of that wire put off 12 volts at all times. I insulated these until the issue can be resolved.

Long story short this method seems to work partially. The glow plug lights went out, and brake light function has returned. I now only get 12 volts when the pedal is depressed. Its not fixed, but now at least I can get the interior and headliner reinstalled, and drive this turd across Texas 5 hours for Thanksgiving dinner. I put a fuseable link in this new ghetto fix for safe measure. After we get back Friday, I'm going to tear the dash out. I'll keep updating this thread until this issue is fully resolved. I cannot stand reading through unresolved threads, drives me nuts

Bret
 

Bret2094

Member
Joined
Jun 25, 2018
Location
College station, TX
TDI
1999.5 Jetta , 2002 Jetta,2003 Jetta Wagon, 2003 Jetta Wagon Non sunroof
Happy Thanksgiving...
Thanks! I hope yours was relaxing. We just got back to college station. Wound up doing 800 miles round trip in the car after driving to see other relatives while in the area. Other than developing a major power steering leak in the rack, the trip was uneventful. We noticed on the trip that quite a few of the lights that normally illuminate the dash were non functional , so I am hoping that when I take the dash out here in a little bit, we find that somewhere that those two circuts are shorting together. Too soon to tell.

Bret
 

Bret2094

Member
Joined
Jun 25, 2018
Location
College station, TX
TDI
1999.5 Jetta , 2002 Jetta,2003 Jetta Wagon, 2003 Jetta Wagon Non sunroof
Looks like I'm about to revive my own dead thread. Over the last couple of years I have tried numerous things to resolve my constant flashing glow plug light situation to no avail. I have had to drive this car for the last 2.5 years with the red/black wire bypassed in order to have functional brake lights. Every once in a while i can drive the car and the lights will be out and the cruise control will work for about 5-10 minutes before the gp light returns. Regardless of what i do, how the wiring is ran or what brake switch i install, I get 00741 Brake pedal monitoring - implausible signal. what else could send signal to the brake pedal? the ABS pump/ module? Im ready to make sure this gets fixed and stays fixed


Bret
 

Stupendous60

Veteran Member
Joined
May 18, 2019
Location
.
TDI
.
Bret, you doing this yourself?
1. The schematic shows fuse 13 feeds battery voltage to the brake switch.
Unplug brake switch and verify you have battery voltage on the red/brown wire.
If you do, remove fuse#13 and see if voltage drops to zero. It should.
If voltage goes to zero you have proven the power side of the circuit.
2. While brake switch is disconnected, check for voltage on the red/black wire. It should be zero volts.
Plug the brake switch back in.
Do the lights come on without the brake pedal being pushed? That would indicate a bad brake switch or another wire feeding voltage into the circuit.
That is all there is concerning the illumination of the brake lamps.
On to implausibility............
Fuse#13, feeding the same red/black wire as above, feeds terminal 18 of the ABS module.
This same red/black wire lets the ABS module know there is a braking event-simply put, your foots on the brake, brake lights on, cruise disengaged.
Implausibility is the ABS module is either seeing a brake pedal "on" signal when it shouldn't or not seeing one when it should.
From what you have posted, it seems the ABS module sees voltage @terminal 18 while the accelerator pedal is pressed/engaged (while driving) while also keeping cruise disengaged.
Do you have a scan tool capable of ABS?
In short, find out if you have voltage on the red and black wire with out the brake pedal pressed. If you do, find the bastard wire feeding the circuit.
Also according to the diag info, glow plug flashes (you know that) and- throttle response intermittent, reduced performance.....
 
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