Reverse lights... Reverse polarity?! ***

Chris_TDI_98 · Oct 22, 2018

Quick question for you experiences with the wiring diagram for the rear reverse lights.
Are the rear reverse lights SUPPOSED to be reverse polarity according to the wiring diagram (which I don’t have)?!
Center pin NEGATIVE, ground/shell POSITIVE?!
Trying to find out if my previous owner mucked something up and resulted in reversing the polarity of the rear reverse lights??
I want to make it be the NORMAL polarity, unless VW did indeed design the car to have rear reverse lights wired in reverse polarity...!?

ToddA1 · Oct 22, 2018

I seriously doubt it. Get a voltmeter to verify.

-Todd

Steve Addy · Oct 22, 2018

The outer cylinder portion of the bulb should never be positive. If it is on your car then someone has mucked it up.

Steve

RabbitGTI · Oct 22, 2018

Unplug it at the transmission and use the brake lights as back up lights. That was my solution. you have to mix in a little "back and pray" too.

Chris_TDI_98 · Oct 23, 2018

ToddA1 said:
I seriously doubt it. Get a voltmeter to verify.

I did. When I made the original post, it was after having verified with the voltmeter. It’s wired with reverse polarity! This explains why today’s new arrival “reverse light LEDs” were failing to light up. Filaments don’t mind about polarity, yet most LEDs do mind. (Other LEDs have electronics built in that accept either polarity just as filaments do.)
Will trace this back tmrw to fuse panel if I must and fix it.

Jetta SS · Oct 23, 2018

I ran into the same thing. I was too lazy to try to figure out a fix.

Jetta_Pilot · Oct 24, 2018

My suggestion would be to trace the wires back as far as possible and see if there is/was a new socket spliced in ! My former 2002 Jetta had brown wires as the ground wire.

ToddA1 · Oct 24, 2018

Chris_TDI_98 said:
Will trace this back tmrw to fuse panel if I must and fix it.

Easier to cut and splice at the light panel, if you’re not particular about it.

Jetta_Pilot said:
My former 2002 Jetta had brown wires as the ground wire.

Brown or brown with tracer, is standard ground color, from what I’ve seen on my VWs.

-Todd

Chris_TDI_98 · Oct 24, 2018

One wrinkle in the equation is, I’ve installed an electronic trailer light module in the trunk area by splicing onto the rear left tail light harness. It’s rather simple electronic module which powers the trailer lighting harness based on the state of the three separate rear lights (tail lights, brake lights, and turn signals), deciding logically whether the left or right trailer light should be off (car lights off), low brightness (tail light), high brightness (brake or turn signal). Could it be the cause of reversing the polarity? I doubt it but asking anyway maybe you guys have some insight.

Jetta SS · Oct 24, 2018

I'd be willing to bet they're all reversed. I did the same as you last year, bought some led's off ebay hoping to have brighter reverse lights. When they didn't work, tested with dvom finding the reverse polarity on the car.

Chris_TDI_98 · Oct 24, 2018

Anyone here got VW contacts on LinkedIn ? Can we ask the VW mk3 vehicle electrical system design team Why TF they engineer the reverse lights to run off positive ground ie reverse polarity ?

ToddA1 · Oct 24, 2018

Jetta SS said:
I'd be willing to bet they're all reversed.

My B4V definitely isn’t, but maybe Jettas are.

-Todd

Mongler98 · Oct 26, 2018

NO, defiantly not
I dint know of any car, let alone a light socket that has the outer casing the + or common. EVER

Jetta SS · Oct 31, 2018

Saw on vortex they go to the connector inside the trunk and cut off the Locking tabs so that the plug can be plugged in backwards. Alternatively they are using a pin extractor to pull the wires out of the plug to reverse them that way.

ToddA1 · Oct 31, 2018

Mongler98 said:
NO, defiantly not
I dint know of any car, let alone a light socket that has the outer casing the + or common. EVER

Jetta SS said:
Saw on vortex they go to the connector inside the trunk and cut off the Locking tabs so that the plug can be plugged in backwards. Alternatively they are using a pin extractor to pull the wires out of the plug to reverse them that way.

Interesting, that this has occurred enough times that threads are created, about it.

-Todd

Vince Waldon · Oct 31, 2018

Jeebus, there's no "polarity" to an incandescent light .

The bulb socket in its plastic housing doesn't care, the filament doesn't care, the electrons could not care less which terminal they flow into or out of, and the engineers that designed it in the early 90s (actually more like the 70's or 80's) were not worried about it either.

Nor did they have future vision that several decades later there's be a mad rush to jam LEDs in there.

GoFaster · Nov 1, 2018

Vince Waldon said:
Jeebus, there's no "polarity" to an incandescent light .
The bulb socket in its plastic housing doesn't care, the filament doesn't care, the electrons could not care less which terminal they flow into or out of, and the engineers that designed it in the early 90s (actually more like the 70's or 80's) were not worried about it either.
Nor did they have future vision that several decades later there's be a mad rush to jam LEDs in there.

True, but by convention, the easily touched with a finger outer shell of the socket is ground/common, and the harder to touch, buried inside center pin is switched hot/positive.

It doesn't matter so much for 12 volt circuits (which don't present much of a shock hazard), but it matters a lot for 120v AC circuits which represent a more significant shock hazard. The easily touched outer shell is on the "common" (which is grounded at the distribution panel thus not presenting a shock hazard), the hot inner pin is more protected.

That carried over to 12 volt circuits by convention.

Chris_TDI_98 · Nov 1, 2018

I called my local VW dealer, service manager.
He said, Heck no, no reverse polarity, that would be nuts, the outer shell contacts of the rear end bulbs should be negative ground, just like the rest of the car. He then admitted that multiple standards exist for example he tried replacing bulbs in his VW and got the bad luck of a slightly different bulb number which reversed the position of high beam and low beam contacts on the base of dual filament bulbs, so he ordered another set from a different manufacturer and they worked. But obviously he was referring to filaments which are unaffected by reverse polarity.

Digital Corpus · Nov 2, 2018

No need for cutting and splicing. Just swap the pins in the terminal that are providing power…

Chris_TDI_98 · Nov 4, 2018

I suspect, and will verify today, that the Mexico VW mk3 factory assembly line tech who originally connected the tail light trunk wiring harness to the fuse relay panel on this car, he/she connected these power wires in reverse polarity, yet the reverse polarity mistake went undetected because the filament tail lights still powered on OK while running reverse polarity!
In my opinion this is the simplest and therefore most plausible explanation for this wiring error which has gone undetected until now.
Except for the presence of excessive RF noise on the battery power lines both while the car is off and while it’s running, which are supposed to be 100% clean DC battety power.

ToddA1 · Nov 4, 2018

Dude, stop overthinking and over complicating things. Swap the wires and be done with it.

-Todd

Chris_TDI_98 · Nov 4, 2018

ToddA1 said:
Dude, stop overthinking and over complicating things. Swap the wires and be done with it.

Of course. I’ll swap the wires one time on the fuse panel and keep the right wire color code vs 4x on the rear wiring plugs and mess up the wire color code.

RoseBud68 · Nov 4, 2018

todda1 said:
dude, stop overthinking and over complicating things. Swap the wires and be done with it.

-todd

lol....

Mongler98 · Nov 5, 2018

Vince Waldon said:
Jeebus, there's no "polarity" to an incandescent light .
The bulb socket in its plastic housing doesn't care, the filament doesn't care, the electrons could not care less which terminal they flow into or out of, and the engineers that designed it in the early 90s (actually more like the 70's or 80's) were not worried about it either.
Nor did they have future vision that several decades later there's be a mad rush to jam LEDs in there.

You are forgetting that this fact is completely dependent on what brand of blinker fluid you use!

turbodieseldyke · Nov 5, 2018

ToddA1 said:
Dude

+1. But hey, at least he didn't make this thread a poll.

I personally hate driving behind anyone with LED taillights, at night. Prius and Cadillac are especially bad, almost blindingly bright.

Mongler98 · Nov 5, 2018

turbodieseldyke said:
+1. But hey, at least he didn't make this thread a poll.
I personally hate driving behind anyone with LED taillights, at night. Prius and Cadillac are especially bad, almost blindingly bright.

ever get behind an ambulance or firetruck, >9,999 lumens of red light in your face!

Digital Corpus · Nov 5, 2018

It’s because most of those LEDs don’t have an even 360° spread but instead cover a 30° to 60° cone. For practicality, lux is a better unit over lumens.

turbodieseldyke · Nov 7, 2018

Mongler98 said:
ever get behind an ambulance or firetruck, >9,999 lumens of red light in your face!

Never noticed, as I'm one of those crazy people who pulls over to the right, waits for them to pass, and follows behind a couple hundred feet back.

Mongler98 · Nov 8, 2018

turbodieseldyke said:
Never noticed, as I'm one of those crazy people who pulls over to the right, waits for them to pass, and follows behind a couple hundred feet back.

NO, not the siren lights and what not, there are plenty of times an ambulance and or fire truck is not in an emergency to get somewhere (usualy back to base), you don't get over unless the sirens are going.
I love about 7 miles from a hospital and its very common to be behind one. those tail lights are like the arc of the covenant bright, my face feels like its melting!

Reverse lights... Reverse polarity?! ***

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