LED Tail/Brake Light Help Needed - '63 Bug 6v

[OldSchoolVW's]

I’m switching to LEDs for my turn signals and tail/brake lights. The turn signals and dash indicator work fine, but I’m not having luck with the tail/brake lights. The incandescent bulbs work correctly … dim when light switch is ON and bright when brakes are applied. When I install LED bulbs that are equivalent to the dual filament incandescent bulbs, the only time the LED bulb comes on is when the brakes are applied. I have contacted the supplier to see what would be needed to get the LEDs to behave as the incandescents do. They have suggested that I “may” need 6 ohm 25 watt LED load equalizers on the brake light wires and “maybe” on the tail light wires as well. “May” and “maybe” ideas sound like they really don’t know and just want me to throw parts at it … at my expense of course.


With the ignition switch in the ON position, these are the readings I get on my meter:

Brakes OFF & Light switch OFF:
Left contact = 0v Right contact = 2.5v


Brakes OFF & Light switch ON:
Left contact = 5.8v Right contact = 2.5v
*The LED bulbs should be on low light in this situation. They are not on at all.


Brakes ON & Light switch OFF:
Left contact = 0v Right contact = 5.6v
*The LED bulbs are on and bright.


Brakes ON & Light switch ON:
Left contact = 5.8v Right contact = 5.6v
*Again, the LED bulbs are on and bright.


I may very well need load equalizers, I’m just hoping those of you who have done this or have a greater understanding of the electrical issues in this situation can give more definitive guidance on how to make these LEDs behave like the incandescents do. Thank you!

_________________
Tom

"Following distance is proportional to IQ."

'63 Beetle Sedan
'69 Beetle Sunroof
'70 Beetle Sedan
'73 Type 3 Fastback

[EVfun]

Your tail lights, brake lights, and parking lights should not require anything special to be swapped out for LED bulbs. The turn signals may not work if you swap in LED bulbs without adding load resistors.

I think the stray 2.5 volts on the brake light terminals when the brakes lights are off may be the problem. It is hard to know what the manufacturer put inside your LED bulbs. If you can find and get rid of that voltage the bulbs may work correctly. It should be about 6 volts with the brake lights on, but 0 volts when the brake lights are off (like the tail lights).
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[OldSchoolVW's]

Thanks EV. The right contact (where the stray 2.5v is) is connected to the black wire which leads back to the brake switch (J3 on the wiring diagram) and then to the fused side of #8. So, maybe a faulty brake switch that is letting voltage leak through? '63 models don't have a brake warning light like my '69, so nothing on the dash to tip me off.

BTW ... When I installed LEDs for the turn signals, I also used the recommended flasher, which is compatible with the LED bulbs. They work perfectly. I had to replace the original bulb holder for the dash turn signal indicator with the later style plastic one with 2 terminals so I could connect the + and ground wires with the correct polarity for the LED dash bulb. After that, the dash bulb worked fine and came on at the same time as the turn signal bulbs.

I'll see if I can isolate the source of the 2.5v on the brake light wire and share what I find.
_________________
Tom

"Following distance is proportional to IQ."

'63 Beetle Sedan
'69 Beetle Sunroof
'70 Beetle Sedan
'73 Type 3 Fastback

[zerotofifty]

Take the volt readings without the led bulbs installed, rather regular bulbs.
Note that low volts on the brake filaments maybe result of poor contacts in the turn switch assembly, even when no turn is requested at the switch. The brake lamp power passes thru the turn signal switch.

Good luck
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Give peace a chance. No American war with Russia!

[OldSchoolVW's]

[EVfun]

My working theory is that your LED bulbs are “smart.” They see the small voltage on the brake light pin as a request to shine on brake light mode, however, 2.5 volts is not enough for them to light. When the tail light power is on they see it as a request for full tail light plus brake light brightness. Since power is available (from the tail light side) it can light up to maximum brightness.

Your turn signal switch should have nothing to do with your tail lights, unless your tail light housing isn’t making a good ground connection.
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[zerotofifty]

[KTPhil]

Double-check the grounding of the lamp assembly. Sounds like it's finding ground through the "filament" of another bulb or filament, and the partial voltage is what you are seeing (2.5V).

Those look really cleaned so it's doubtful, but I always check the free/easy faults first (or again).
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Current Fleet:
'71 Fastback
'69 Westfalia
Retired:
'67 Beetle
'65 Beetle (x2)
'65 Bus
'71 Squareback

[OldSchoolVW's]

[OldSchoolVW's]

[OldSchoolVW's]

[EVfun]

[OldSchoolVW's]

[EVfun]

[OldSchoolVW's]

[OldSchoolVW's]

Update ...

So I put the LED tail/brake light bulbs back in to test them, turned the ignition to "ON" and turned on the light switch. To my surprise the tail lights came on at the lower intensity as they should. Then I pushed on the brake pedal and they got bright. This is the first time they have behaved as they are supposed to. The last time I tested them, I got no low intensity tail light ... just the bright intensity when the brakes were applied. I did nothing to the wiring, so I'm guessing it was the brake switch on the master cylinder that was sticking and letting the 2.5v get through which was messing with the LEDs as EV suggested. The brakes are working well, so I'm just going to let the MC be. Since the reliability of the MC brake light switch is questionable, I am inclined to go ahead and install the pedal activated brake switch mentioned earlier and take the MC switch out of the picture.

Thanks to you all for the advice and tips!
_________________
Tom

"Following distance is proportional to IQ."

'63 Beetle Sedan
'69 Beetle Sunroof
'70 Beetle Sedan
'73 Type 3 Fastback

[herbie1200]

I had a similar problem with 6v led bulb.

The issue:when lights are on and stop pedal is not pressed, the LED put out some current ALSO from the wiring for the stop function. In fact while the filament bulb has 2 separate filaments, the LED has only 1 emitter, driven to make high or low light.
But the wiring in the car connects the 2 stoplight in parallel.

My solution was to insert a couple of diodes (one foreach side) in series with the stop contact.

The arrangement: buy 2 diodes and sold a male and a female spade connector at diode terminal, then put this circuit between the wiring from the car and the terminal on the rear light... all OK!