legends,
I have a 72 pontiac lemans resto mod project that I will be incorporating 2020 defender tail lights.

I have some questions about the wiring and the voltage in particular. I have a diagram and know where the power should be sent for all functions, but it looks like the voltage is sent from the BCM. I need to know if the BCM is stepping down the voltage before feeding the tail light circuit board. The wires at the connector are very thin guage (20-22). I don't want to fry the board/leds by assuming I can feed straight 12v power

Any help/knowledge would be greatly appreciated!

 

You probably already know this but the wiring isn't like it used to be where each bulb had a discreet 12v power circuit switched from a remote stalk or switch.

There's a can bus that communicates commands to the board in these lights and just 1 power wire running to the entire assembly. That board routes the power based on data it receives on the bus consisting of many modules.

It would seem to me that you would have to either find a way to replicate those commands or find a way to remove that board and run dedicated switched power wires to each bulb in the assembly.. Is that what you're trying to do?

If the bulbs have their own boards to manage power, you might be okay but, if not, you will need an electrical nerd to figure out the resistors you'll need to limit the current. If you can get the data sheet on the bulbs, you'll need forward current, supply voltage, and forward voltage for the bulbs. It won't be that hard to calculate with that info but getting it sounds like a long shot.

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I'm no help, but let's see the Pontiac!

 

Couple of things here, I agree that there are Canbus signals (this is how all modules communicate), but the canbus signal is still only the "switch". Can-bus signal wires do not carry or send power or ground. The tail light is still operated by power.

You are still right, though, that i am looking for the voltage that is sent from the BCM to the taillight after it has receives a canbus signal to turn on a brake light, running light, etc.

Also, there isn't a "bulb" or bulbs, its a series of LED lights that operate on their own integrated circuit board within the tail light assembly. It is likely that the board is set up to take a 12V signal and any voltage reduction is performed with circuitry on that board. Its an expensive gamble to guess whether it is done there or at the BCM..

 

Have you got wiring diagram? It's still 12V signal, amperage is different story, but there's no DC-DC conversion.
Each has feed line and ground.

 

I think that board in the light assembly is reading can bus signals and switching the lights based on the data. I'm 60% sure you can't just put power to it and get working lights without the data trigger. It's like a computer can power speakers but it requires software, input device, and a sound file. You can pull the speakers out and connect them to an analog amp but the amp can't go through the computer first.

That board in the assembly would probably have to be removed and replaced with resistors that limit the current. LED's are like dogs. They don't stop eating. They'll pull current until they blow. Voltage matters but current is an instant led killer.

Do you have pictures of the inside of this thing?

 

Getting inside is going to require some surgery. I can see through the front of the lense and it looks like a ton of surface mount resistors. Also, I see this printed on the back....

 

The BCM sends just 12v to the rear lights, you should be good.
But better be safe and test before of course.
Nice project !

 

Funny, the rear taillights are perfectly safe for can bus injection theft, but front headlights are not, CAN bus goes there.

 

I saw this online and I was really skeptical that it was accurate. Partly because my connector has 4 black wires at the tail light and this connector showed 5. I do not have the harness side. But, I figured it out tonight. The UK version has a separate wire for turn signal and the US version uses 1 wire for the stop and turn (same light function).

I rigged up a 1 amp protected circuit from a pdm i had laying around and sent 12v to pins 1 through 3, and ground to pin 4. Everything worked as it should.

Thanks all! Great sounding board situation