LEDs: brake light barely brighter than tail light…

[ErrorMargin]

A previous owner of my 84 targa replaced all the exterior lights with LEDs. Everything works fine, except that I just today realized that when I have the headlights on, the brake light is hardly at all brighter than the tail light.

The brake light and tail light are in the same position and I’m guessing use the same bulb.

Any ideas about what is causing this?

Update - 25 Jan 25
Issue fixed, see this post: https://forums.pelicanparts.com/porsche-911-technical-forum/1172489-leds-brake-light-barely-brighter-than-tail-light.html#post12398142

[917_Langheck]

Have the same issue in my 84. Did Spoke's mod to the proper led flasher and still have hyperflash issues front and back, even with John Audette's canbus LEDs.

For the brake lights some have said it may be related to the master cylinder senders. Others have said it's a ground issue. Early leds need a resistor (~50 Ohm) in the circuit. I think it may need a separate diode as well to prevent back feed.

The real PITA about all this is some cars have no issues at all with the change over. Very frustrating.

[GH85Carrera]

I left my driving lights and turn signals alone, as they are plenty bright.

I put in Spoke's LED board and the resistor he sells to keep my cruise control to keep working. The brake light are BRIGHT. I have had other G body drivers ask about how bright they are.

[ErrorMargin]

Originally Posted by GH85Carrera

I put in Spoke's LED board and the resistor he sells to keep my cruise control...

Tell me more. You need a resistor to keep the cruise control working? Maybe that is why my cruise control is not working.

[Jeff Higgins]

Originally Posted by ErrorMargin

A previous owner of my 84 targa replaced all the exterior lights with LEDs. Everything works fine, except that I just today realized that when I have the headlights on, the brake light is hardly at all brighter than the tail light.

The brake light and tail light are in the same position and I’m guessing use the same bulb.

Any ideas about what is causing this?

Yes, they are in the same position and use the same bulb.

I'll bet that the problem is the previous owner used cheap auto parts store LED replacements for the standard 1157 dual filament bulbs. I've found many of those to simply not have much of a difference between "bright" (for brake or turn signals) and their normal running light brightness. Nothing wrong with the car, nothing you can do about it other than replacing them with higher quality LED bulbs that provide a greater delta.

[famoroso]

This is the way...
https://www.spokeworksled.com/

http://forums.pelicanparts.com/porsche-911-technical-forum/854989-led-brake-lights.html

http://forums.pelicanparts.com/porsche-911-technical-forum/1053456-spokeworks-led-brake-light-review.html

More expensive than FLAPS offerings and those cringey LED tower bulbs, but worth every penny, and then some. Especially as their design does not rely on 30-40+ year old reflectors that may no longer be so... reflective.

[rothaus]

Here is an example of my 82 SC with the LED for Tail/Brake lights installed.



I also made a little setup since the surface of the tail/brake light is relatively small on these 911. Now the turn signal bulb comes on together with the brake light and gives a larger surface for the brake lights.



Engelbert

[GH85Carrera]

Originally Posted by ErrorMargin

Tell me more. You need a resistor to keep the cruise control working? Maybe that is why my cruise control is not working.

Contact Spoke. He has the proper resistor and instructions to put it in. It is vital to make cruise control to work. It senses the brake light lights to shut off cruise control.

[spoke]

Originally Posted by ErrorMargin

Tell me more. You need a resistor to keep the cruise control working? Maybe that is why my cruise control is not working.

If you have LED brake lights including the 3rd brake (if mounted) is LED, the cruise control will not function.

The diagram below explains the operation of the CC and why it doesn't work with LEDs. The CC senses when the driver presses the brake pedal by monitoring the brake light voltage. The CC dumps about 17ma of current into the brake bulb. Incandescent bulbs are very low impedance so dumping 17ma into the bulb hardly generates any voltage. Maybe millivolts.

But when the brake lights are LEDs, the LED impedance is much higher (less current) and the LEDs I make have 4 LEDs in series. Each LED needs about 2V to turn on and will light with 1ma. 17ma will turn them on and the voltage across the brake LEDs will be about 7-8V. Not sure what voltage other aftermarket LEDs will drop.

With anything more than a couple of volts on the brake light and the CC thinks the brake are on and will always be off.

The only solution is to use high power ballast resistors normally used to calm flasher relays when turnsignals are LEDs. I make a pigtail with high power ballast resistor which goes between the brake switch and the brake lights.

[spoke]

Originally Posted by rothaus

Here is an example of my 82 SC with the LED for Tail/Brake lights installed.



I also made a little setup since the surface of the tail/brake light is relatively small on these 911. Now the turn signal bulb comes on together with the brake light and gives a larger surface for the brake lights.



Engelbert

Excellent to let the rear turnsignal double as running lights. This can only be done with red turnsignals as amber running lights are prohibited in the rear of the vehicle.

To allow the rear RED turnsignals to double as running lights, I steal running light power from the rear sidemarker and tether the sidemarker to the rear turnsignal.

[spoke]

Originally Posted by 917_Langheck

Have the same issue in my 84. Did Spoke's mod to the proper led flasher and still have hyperflash issues front and back, even with John Audette's canbus LEDs.

Would you please expand on the flasher relay and hyperflashing? If using EP26 or EP36 there should be no hyperflashing.

[rothaus]

Originally Posted by spoke

Excellent to let the rear turnsignal double as running lights. This can only be done with red turnsignals as amber running lights are prohibited in the rear of the vehicle.

To allow the rear RED turnsignals to double as running lights, I steal running light power from the rear sidemarker and tether the sidemarker to the rear turnsignal.

Take another look at the video.
On the black car example the turn signals are used together with the brake lights, so the lighted surface is a lot larger as the brake light alone. A soon the turn signal comes on, the turn signal for that side starts to flash and the other side stays solid.

In the meantime I did it to the white 911 as well.

Engelbert

[spoke]

Originally Posted by rothaus

Take another look at the video.
On the black car example the turn signals are used together with the brake lights, so the lighted surface is a lot larger as the brake light alone. A soon the turn signal comes on, the turn signal for that side starts to flash and the other side stays solid.

In the meantime I did it to the white 911 as well.

Engelbert

Interesting. So you've tapped into the turnsignal as extra brake. How did you interrupt the brake to flash the turnsignal? I did this on the front turnsignals. It gets weird because it's impossible to determine when the turnsignals stop because they are always stopping to flash except the last flash the power on the turnsignal wire just goes away forever.

[ErrorMargin]

Originally Posted by ErrorMargin

...when I have the headlights on, the brake light is hardly at all brighter than the tail light.

The lights from Spoke mentioned above are super cool!

I found that the Sylvania Zevo 1157 Red bulbs work well and have a large difference in brightness between running light and brake light.

The only issue is that due to the constant voltage from the cruise control on the line described above, these LEDs are on all the time at a very low level. There is still plenty of differentiation between running light and brake light, and I regard the low level on as a sort of daytime running light.

I had to use a dental pick to bend the contacts inside the housing forward a bit to get firm contact on the bulb so they would not rattle.

You can see the test in the video below, note that when I turn on the car the bulbs immediately run at a low level due to the cruise control issue mentioned above.