2 questions -If you are worried about the factory wiring at all (or any backfeeding) put a diode on the high beam wire before the relays (so the power will only go towards the relay).
Ok, I'll just use the relay. It won't be used too often so hopefully there will not be any issues.Google diode and/or look on elb for specifics on that inquiry. I don't know what specific diode you'd require but its basically an electronic device which only permits electricity to flow one way.
Drawing power from the high beams- if you are only using it to trigger a relay, I would not worry. If you are using it for anything more than a trigger and/or to power anything other than the OEM high beams, I would worry/not do it at all.
The diode would prevent any random/stray currents (electricity) from flowing back into the high beam wire, which could in theory bugger with the computer/blow fuses, etc. (on the very off chance the relay shorted out, or the aftermarket light itself, or some other random event).
Ok, so using the diagram you sent me, I shouldn't have any issues. I'll be doing this install hopefully tomorrow.With the high beam connected to the coil of the relay, the only voltage is from the high beams. A diode would not help as it would need to be placed in series with the relay coil and serve no useful purpose, as the polarity would have to be to allow the +12 volts from the high beams to flow to the relay. With nothing other than the high beam power and ground connected to relay coil there will be no voltages feeding back toward the high beam connection of the headlights.
