Can two brake lights work off one wire???

My 2004 Jetta wagon has had an intermittent passenger side brake light for a while. I've replaced the bulb (more times than I can remember), brake switch, bulb housing, even trying a non-VW brand one, because the design for these is dumb. I know I have a break in the wire somewhere between the front bumper, and rear bumper (sarcasm detected...)

To save me time pulling all my plastic body panels off, and other pieces (dash? or wherever it goes), can I just run a jumper wire from the properly working driver side brake light?

Any electric pros out there know how many watts/amps each side can take and if for the brake light on the DS, can it take both without blowing a fuse????

I have a Bentley, but I don't think it tells me how many watts or amps that circuit can take. I think this is an electrical engineer type question.

Thank you!

My 03 has 1 wire going to the back and it branches off to the 3 brake lights.
I would think (ut oh) the split off would be in the back on the drivers side rear.
Did you check the ground connection on the problem side? Clean and shiny?

Yep, that would work fine.

The ECU monitors both the Left and Right brake light bulbs (but not the one in the back glass). When both bulbs blow or lose ground, the GP light will flash continuously when the ignition is ON.

It's been a while since I took a look at the schematics. but, I believe as long as your changes don't affect the ECU monitoring, as others have said, it should work fine!

AndyBees said:

The ECU monitors both the Left and Right brake light bulbs (but not the one in the back glass). When both bulbs blow or lose ground, the GP light will flash continuously when the ignition is ON.

It's been a while since I took a look at the schematics. but, I believe as long as your changes don't affect the ECU monitoring, as others have said, it should work fine!

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On my 03 its 1 wire going to the back and teeing out to the 3 lights.
I suspect it senses the current total.
This is why I had to install load resisters for LED lights.

When it acts up have you checked for voltage and a good ground? Does the turn signal still work on that bad side? My Beetle used to eat bulbs and my son took the socket out and tightened the socket by bending the tabs that hold the bulbs. Factory and aftermarket bulbs are different with the factory fitting the socket tighter. Had the blinking GP light that tipped me off to both of them being burnt out the last time. It has been 6 months since my son fixed it.

Wonneber, I installed a single bulb under the back seat of my Van (ALH engine) to keep the ECU happy.

Looking the binder of schematics for my project, in the single wire from the Brake Switch going to the rear, there is a splice (labeled as A18) before it branches to the two brake lights . The circuit leaving Splice A18 goes to Pin 32 of the ECU.

So, that must be where the monitoring of the brake lights comes into play. And, considering the High Mount Brake Light is in the same circuit, I suspect resistance is probably how the ECU detects both lights are blown, as you suggested. Thus, my single bulb must be high wattage, otherwise the ECU would not be happy!

A while back I read something about not using the old 1157/1156 bulbs for the newer numbers 2xxx, 7xxx & such bulbs.
Something about the contact length at the bottom of the bulbs not being long enough and the wattage.
Maybe bite the $$$ bullet and buy the 7528 bulbs?

AndyBees said:

Wonneber, I installed a single bulb under the back seat of my Van (ALH engine) to keep the ECU happy.

Looking the binder of schematics for my project, in the single wire from the Brake Switch going to the rear, there is a splice (labeled as A18) before it branches to the two brake lights . The circuit leaving Splice A18 goes to Pin 32 of the ECU.

So, that must be where the monitoring of the brake lights comes into play. And, considering the High Mount Brake Light is in the same circuit, I suspect resistance is probably how the ECU detects both lights are blown, as you suggested. Thus, my single bulb must be high wattage, otherwise the ECU would not be happy!

Click to expand...

I just looked again, my diagram shows the 3 in back joining at the same point then going to the switch.
There does seem to be another joint in front (I think) but no other wires going to it.

I like the idea of using a bulb as the load.
Would have saved me a few bucks.

"When it acts up have you checked for voltage and a good ground? Does the turn signal still work on that bad side?"-Yes, but since it is intermittent, it show good 99% of the time. It only goes bad when driving (from a break in the wire somewhere).

I think I'll try and run the PS light off the DS and give it a shot!

I disconnected the maligned passenger side brake light wires and ran a jumper for the +/- to the driver side brake light. So far, so good, no blown fuses expected. both sides were a red/black for the positive, and brown for the negative, so probably are the same positive in the car anyway!