Mk4 LED brake lights

[YellowLemon]

I put red LED bulbs for the brake lights for the much faster response time, and also soldered some diodes to have the fog lights come on as brake lights - pictures below.

Does anyone know why the brake lights and outer LEDs in the middle/upper brake light glow faintly? It's only when the ignition is ON. When the ignition is OFF, there is no glow, but the brakes still work fine. In the wiring diagram I can't reconcile why this is: it's just simple circuit with a switch. There must be something else going on, that's not documented in the diagram.....

In the later VW there is a small current running in the circuits for cold diagnosis to detect blown bulbs. But this mk4 doesn't have a bulb detection system AFAIK. (ie. when I take some brake bulbs out, no lights are triggered in the dash, anyway)

Brakes only:


Parking lights only:


Parking + brake lights:


No lights, ignition OFF:


No lights, ignition ON:

[YellowLemon]

This is the wiring diagram I'm using, for Golf July 2000 - Sep. 2001:
The brake circuit is a simple switch with bulbs. The right/left/center lights are all on the same circuit, and not broken up into separate sides (unlike the newer VW which drive the lights per side to detect blown bulbs)


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And these are the P21W bulbs I am using in the tails: (from Blingworks Melbourne)

[dylan8]

When I installed interior LED lights in my Mk4 some would glow even when off.
Something to do with the car running a low amount of power all the time, normal globe isnt powerful enough to run off it, where as a LED is.
Not sure if the same applies, as you have mentioned?

[JustCruisn]

There must be some current on that line, probably for bulb failure alert.
Try adding a resistor to the circuit and see how it goes. Try a few different values.

[YellowLemon]

When I installed interior LED lights in my Mk4 some would glow even when off.

Ah yes, thanks for the info! So it's not only the brake circuit.... I was thinking of putting some interior LEDs myself

I'll put one of those big 'load balancing' resistors (from a separate CANBUS LED kit) in the brake circuit and see what happens. The glow doesn't really bother me, I'm just curious why it's there

[dylan8]

Didn't bother me either. I'd just be careful with the brakes glowing that the police don't give you a hard time

[YellowLemon]

Thanks Dylan! The glowing brakes are barely noticeable & only at night, not at all during the day. I've had 3 cops in Victoria (the pickiest cops in the country I believe) drive behind me for a long time, no problems so far. Will update here if there's any change