Ok... my curiosity is... piquée...
I'll be tapping into my high beam wire, to trigger a relay for some auxiliary lights, soon. This is the first time I hear of such a device, and also the first time I hear tapping into the high beam wire could cause... something...
Electronics semi-noob here so be gentle please, haha. What are potential problems of tapping into this wire ? In my case, I would only want to trigger a relay.
The high beam is not run on a solid 12v source... it has a PWM (pulse width modulated) source. This is used by the computer to detect when lamps are out or damaged. There are only a few relays I have found that will stay activated when using this type of hot. Most will chatter (bounce on/off very fast) or buzz. Even though they buzz, some will stay activated enough to turn on what-ever you are running, but the relay will get hot and not last long.
Provided you find a relay that will stay activated, you are adding circuitry that changes how the computer views the lamp circuit. It may be okay, or it may throw a diagnostic message. In the case of JK fog lights I have seen the computer deactivate the circuit all together.
By adding the capacitor and diode to the relay's circuit we can isolate and protect the CANBus side while smoothing out the voltage the relay sees which stops the chatter.
It's not really any magic, and I even post a picture of how the circuit is made. I have just been asked so many times to make these I finally did.
If you want to go "science fair project" and make your own I'm happy to help with that too.
Hopefully this helps, let me know if you are still confused.