I always just tap into a wire at the back of the headlight, use a test light to identify the high beam wire, and use that as the trigger wire for the relay.
If your car uses HB3 globes for example they only have one filament, so you need to take the feed off the high beam shutter. Probably with a micro primary relay powering a secondary relay or you will end up with a computer error on the car. A bit more painful with modern cars like my 2013 car.
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Hi mischief,
I attempted to do it on the cheap & tap into the headlight wiring - BUT Isuzu don't add extra wire for the buyer's convenience! I lost some skin, lots of hours trying to do it so I bit my pride & bought a Stedi adaptor - the job was done in minutes!
Still can't see how they could justify $30odd, though.
You can get these adaptors at most auto parts shops these days.
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Warren
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